Clarify when protobuf dependency builds protoc (#20542)

### Description
<!-- Describe your changes. -->
Currently figuring out if the protobuf dependency is building protoc it
is a little obtuse and inconsistent
* in some places we directly set protobuf_BUILD_PROTOC_BINARIES to OFF
to indicate the protobuf dependency is not building protoc
  * e.g. macOS/iOS/visionOS builds
* for a user provided protoc path we don't set
protobuf_BUILD_PROTOC_BINARIES, and inside protobuf_function.cmake that
determines if `protobuf::protoc` is added as a dependency or not
*
0dda8b0c44/cmake/external/protobuf_function.cmake (L40-L45)

To be more consistent/explicit, set protobuf_BUILD_PROTOC_BINARIES to
OFF when ONNX_CUSTOM_PROTOC_EXECUTABLE set and valid.

Remove outdated script that built and external protoc binary which was
used in later builds. The build setup will fetch a pre-built protoc so
there's no need for this additional build.

### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
Make it easier to figure out if protoc is coming from the protobuf
dependency.

cmake/external/onnxruntime_external_deps.cmake

@@ -97,7 +97,6 @@ FetchContent_Declare(
 )
 
 
-
 # Flatbuffers
 # We do not need to build flatc for iOS or Android Cross Compile
 if (CMAKE_SYSTEM_NAME STREQUAL "iOS" OR CMAKE_SYSTEM_NAME STREQUAL "Android" OR CMAKE_SYSTEM_NAME STREQUAL "Emscripten")
@@ -122,6 +121,19 @@ FetchContent_Declare(
     FIND_PACKAGE_ARGS 23.5.9 NAMES Flatbuffers
 )
 
+
+#Protobuf depends on utf8_range
+FetchContent_Declare(
+    utf8_range
+    URL ${DEP_URL_utf8_range}
+    URL_HASH SHA1=${DEP_SHA1_utf8_range}
+    FIND_PACKAGE_ARGS NAMES utf8_range
+)
+
+set(utf8_range_ENABLE_TESTS OFF CACHE BOOL "Build test suite" FORCE)
+set(utf8_range_ENABLE_INSTALL OFF CACHE BOOL "Configure installation" FORCE)
+
+
 # Download a protoc binary from Internet if needed
 if(NOT ONNX_CUSTOM_PROTOC_EXECUTABLE)
   # This part of code is only for users' convenience. The code couldn't handle all cases. Users always can manually
@@ -148,6 +160,7 @@ if(NOT ONNX_CUSTOM_PROTOC_EXECUTABLE)
         FetchContent_Declare(protoc_binary URL ${DEP_URL_protoc_win32} URL_HASH SHA1=${DEP_SHA1_protoc_win32})
         FetchContent_Populate(protoc_binary)
       endif()
+
       if(protoc_binary_SOURCE_DIR)
         message("Use prebuilt protoc")
         set(ONNX_CUSTOM_PROTOC_EXECUTABLE ${protoc_binary_SOURCE_DIR}/bin/protoc.exe)
@@ -164,15 +177,30 @@ if(NOT ONNX_CUSTOM_PROTOC_EXECUTABLE)
         FetchContent_Declare(protoc_binary URL ${DEP_URL_protoc_linux_aarch64} URL_HASH SHA1=${DEP_SHA1_protoc_linux_aarch64})
         FetchContent_Populate(protoc_binary)
       endif()
+
       if(protoc_binary_SOURCE_DIR)
         message("Use prebuilt protoc")
         set(ONNX_CUSTOM_PROTOC_EXECUTABLE ${protoc_binary_SOURCE_DIR}/bin/protoc)
         set(PROTOC_EXECUTABLE ${ONNX_CUSTOM_PROTOC_EXECUTABLE})
       endif()
     endif()
+
+    if(NOT ONNX_CUSTOM_PROTOC_EXECUTABLE)
+      message(FATAL_ERROR "ONNX_CUSTOM_PROTOC_EXECUTABLE must be set to cross-compile.")
+    endif()
   endif()
 endif()
 
+# if ONNX_CUSTOM_PROTOC_EXECUTABLE is set we don't need to build the protoc binary
+if (ONNX_CUSTOM_PROTOC_EXECUTABLE)
+  if (NOT EXISTS "${ONNX_CUSTOM_PROTOC_EXECUTABLE}")
+    message(FATAL_ERROR "ONNX_CUSTOM_PROTOC_EXECUTABLE is set to '${ONNX_CUSTOM_PROTOC_EXECUTABLE}' "
+                        "but protoc executable was not found there.")
+  endif()
+
+  set(protobuf_BUILD_PROTOC_BINARIES OFF CACHE BOOL "Build protoc" FORCE)
+endif()
+
 #Here we support two build mode:
 #1. if ONNX_CUSTOM_PROTOC_EXECUTABLE is set, build Protobuf from source, except protoc.exe. This mode is mainly
 #   for cross-compiling
@@ -183,17 +211,6 @@ else()
  set(ONNXRUNTIME_PROTOBUF_PATCH_COMMAND "")
 endif()
 
-FetchContent_Declare(
-    utf8_range
-    URL ${DEP_URL_utf8_range}
-    URL_HASH SHA1=${DEP_SHA1_utf8_range}
-    FIND_PACKAGE_ARGS NAMES utf8_range
-)
-
-set(utf8_range_ENABLE_TESTS OFF CACHE BOOL "Build test suite" FORCE)
-set(utf8_range_ENABLE_INSTALL OFF CACHE BOOL "Configure installation" FORCE)
-
-
 #Protobuf depends on absl and utf8_range
 FetchContent_Declare(
   Protobuf
@@ -211,10 +228,10 @@ set(protobuf_BUILD_TESTS OFF CACHE BOOL "Build protobuf tests" FORCE)
 #set(protobuf_INSTALL OFF CACHE BOOL "Install protobuf binaries and files" FORCE)
 set(protobuf_USE_EXTERNAL_GTEST ON CACHE BOOL "" FORCE)
 
-if (CMAKE_SYSTEM_NAME STREQUAL "Android")
-  set(protobuf_BUILD_PROTOC_BINARIES OFF CACHE BOOL "Build protobuf tests" FORCE)
-  set(protobuf_WITH_ZLIB OFF CACHE BOOL "Build with zlib support" FORCE)
+if (ANDROID)
+  set(protobuf_WITH_ZLIB OFF CACHE BOOL "Build protobuf with zlib support" FORCE)
 endif()
+
 if (onnxruntime_DISABLE_RTTI)
   set(protobuf_DISABLE_RTTI ON CACHE BOOL "Remove runtime type information in the binaries" FORCE)
 endif()

tools/ci_build/github/apple/build_host_protoc.sh

@@ -1,40 +0,0 @@
-#!/bin/bash
-
-# Note: This script is intended to be called from a macOS pipeline to build the host protoc
-# See tools/ci_build/github/azure-pipelines/mac-ios-ci-pipeline.yml
-# The host_protoc can be found as $PROTOC_INSTALL_PATH/bin/protoc
-
-set -e
-
-if [ $# -ne 3 ]
-then
-    echo "Usage: ${0} <repo_root_path> <host_protoc_build_path> <host_protoc_install_path>"
-    exit 1
-fi
-
-set -x
-
-ORT_REPO_ROOT=$1
-PROTOC_BUILD_PATH=$2
-PROTOC_INSTALL_PATH=$3
-
-pushd .
-mkdir -p "$PROTOC_BUILD_PATH"
-cd "$PROTOC_BUILD_PATH"
-DEP_FILE_PATH="$ORT_REPO_ROOT/cmake/deps.txt"
-PATCH_FILE_PATH="$ORT_REPO_ROOT/cmake/patches/protobuf/protobuf_cmake.patch"
-protobuf_url=$(grep '^protobuf' "$DEP_FILE_PATH" | cut -d ';' -f 2 | sed 's/\.zip$/\.tar.gz/')
-curl -sSL --retry 5 --retry-delay 10 --create-dirs --fail -L -o protobuf_src.tar.gz "$protobuf_url"
-tar -zxf protobuf_src.tar.gz --strip=1
-patch --binary --ignore-whitespace -p1 < "$PATCH_FILE_PATH"
-# The second 'cmake' is a folder name
-cmake cmake \
-    -DCMAKE_POSITION_INDEPENDENT_CODE=ON \
-    -Dprotobuf_BUILD_TESTS=OFF \
-    -Dprotobuf_WITH_ZLIB_DEFAULT=OFF \
-    -Dprotobuf_BUILD_SHARED_LIBS=OFF \
-    -DCMAKE_BUILD_TYPE=Release \
-    "-DCMAKE_INSTALL_PREFIX=$PROTOC_INSTALL_PATH"
-make -j $(getconf _NPROCESSORS_ONLN)
-make install
-popd

tools/ci_build/github/azure-pipelines/android-x86_64-crosscompile-ci-pipeline.yml

@@ -394,14 +394,6 @@ stages:
       - script: brew install coreutils ninja
         displayName: Install coreutils and ninja
 
-      # We build the host protoc to <ORT_ROOT>/protobuf_install
-      - script: |
-          /bin/bash $(Build.SourcesDirectory)/tools/ci_build/github/apple/build_host_protoc.sh \
-            $(Build.SourcesDirectory) \
-            $(Build.BinariesDirectory)/protobuf \
-            $(Build.SourcesDirectory)/protobuf_install
-        displayName: Build Host Protoc
-
       - template: templates/use-android-emulator.yml
         parameters:
           create: true

tools/ci_build/github/azure-pipelines/templates/c-api-cpu.yml

@@ -110,13 +110,6 @@ stages:
       parameters:
         xcodeVersion: 14.2
 
-    - script: |
-        /bin/bash $(Build.SourcesDirectory)/tools/ci_build/github/apple/build_host_protoc.sh \
-          $(Build.SourcesDirectory) \
-          $(Build.BinariesDirectory)/protobuf \
-          $(Build.BinariesDirectory)/protobuf_install
-      displayName: Build Host Protoc
-
     - template: download-deps.yml
 
     - task: PythonScript@0
@@ -130,7 +123,6 @@ stages:
         set -e -x
         python3 tools/ci_build/github/apple/build_apple_framework.py \
           --build_dir "$(Build.BinariesDirectory)/ios_framework" \
-          --path_to_protoc_exe $(Build.BinariesDirectory)/protobuf_install/bin/protoc \
           tools/ci_build/github/apple/default_full_ios_framework_build_settings.json
         mkdir $(Build.BinariesDirectory)/artifacts
         mkdir -p $(Build.BinariesDirectory)/artifacts_staging/onnxruntime-ios-xcframework-$(OnnxRuntimeVersion)