Support MacOS for running MMTk Ruby binding

[dugiahuy]

Description

Currently, MMTk Ruby binding only support development on Linux. However, I want to use my MacBook for support my local development.

Changes

• Implement memory allocation for MacOS
• Fix missing function declaration (only happen when enable debug mode)
• Allow libmmtk_ruby.dylib dynamic library extension for MacOS

[eileencodes]

I tried using this locally on macos and these changes threw an error since it was still trying to load the so file.

The Ruby build system already has code to replace the extension, this can use $SOEXT instead and then you don't need two separate variables.

From my testing, if you change [MMTK_RUBY_SO_NAME=libmmtk_ruby.so] to [MMTK_RUBY_SO_NAME=libmmtk_ruby.$SOEXT] you can build with MMTK on macos and it will use the libmmtk_ruby.dylib.

Note: it builds but doesn't run, mmtk panics, haven't debugged that yet, but it definitely builds 😄

[wks]

I updated this PR and made some small changes, including using $SOEXT as @eileencodes suggested.

@dugiahuy @eileencodes Can you confirm if it still compiles on MacOS with my changes applied?

[eileencodes]

I can confirm this compiles on my mac with your changes @wks.

[dugiahuy]

Thank for your help! @eileencodes @wks 👍🏻 👍🏻