### Description
1. Make 2 cache tasks in one pipeline really works
2. Each building step has its own environment variable CCACHE_DIR
instead of job variables.
3. Extenal Protobuf compilation cache only updates with deps.txt. It
doesn't generate new cache in every commit.
### Motivation and Context
The simple workflow is as below
```
--------build with ccache-------
|
cache
|
{CCACHE_DIR}-----cache stat.
```
```
-------Cache@2------
|
download cache
|
{path}--------upload cache
```
1. {XXX} means environment variable or task input.
2. {CCACHE_DIR} must be consistent with {path}. Ccache produces caches
in {CCACHE_DIR} and Cache@2 download cache into {path} and tar {path}
and upload it.
3. Protobuf changes with deps.txt so that it would reduce the storage
size.
4. Next step, we may split the compilation into 2 steps, one for
external dependencies and another for ORT.
