Allow to select shell in command line for token replacement.

[Jarod42]

What does this PR do?

Allow to select shell type to use for command substitution.
We can use posix shell on windows

How does this PR change Premake's behavior?

Token command substitution uses shell before os.target()

Anything else we should know?

Needed for testing repository to run ninja with msc under windows run from bash shell.

Did you check all the boxes?

• Focus on a single fix or feature; remove any unrelated formatting or code changes
• Add unit tests showing fix or feature works; all tests pass
• Mention any related issues (put closes #XXXX in comment to auto-close issue when PR is merged)
• Follow our coding conventions
• Minimize the number of commits
• Align documentation to your changes

[KyrietS]

When would you need an --os=windows with --shell=posix or vice versa?

[Jarod42]

My use case is --os=windows, when not using cmd prompt, so with mingw/msys.
I have test cases for ninja/gmake2 in my testing repo (https://github.com/Jarod42/premake-sample-projects/actions/runs/8222529226 and https://github.com/Jarod42/premake-sample-projects/actions/runs/8224334172/job/22488026238) respectively (gmake2 has currently other issues...)
codelite/codeblocks might also be concerned.

[KyrietS]

aight, looks good 👍 I've never used msys myself but this change might be helpful

[nickclark2016]

LGTM