Issue #, if available: #3315

Description of changes:

This just shows how to setup mingw-w64 build environment with MSYS2.

This uses GitHub Actions but we'll use internal CI build system instead of GitHub Actions.

The added workflow has 2 jobs. One job applies a patch ( https://github.com/msys2/MINGW-packages/blob/master/mingw-w64-aws-sdk-cpp/aws-sdk-cpp-pr-1333.patch ) in MSYS2 and another job builds aws-sdk-cpp as-is.

Both jobs do the followings:

1. Setup build environment with MSYS2
2. Run cmake
3. Build

I'll add review comments for details.

Check all that applies:

• Did a review by yourself.
• Added proper tests to cover this PR. (If tests are not applicable, explain.)
• Checked if this PR is a breaking (APIs have been changed) change.
• Checked if this PR will not introduce cross-platform inconsistent behavior.
• Checked if this PR would require a ReadMe/Wiki update.

Check which platforms you have built SDK on to verify the correctness of this PR.

• Linux
• Windows
• Android
• MacOS
• IOS
• Other Platforms

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