fix: remove -lm flag for windows native target

[CrazyboyQCD]

Related Issues

• Related issues: can not build hello on window LINK : fatal error LNK1181: m.lib #861

Type of Pull Request

• Bug fix
• New feature
  • I have already discussed this feature with the maintainers.
• Refactor
• Performance optimization
• Documentation
• Other (please describe):

Does this PR change existing behavior?

• Yes (please describe the changes below)
  • Remove -lm flag for building msvc target
• No

Does this PR introduce new dependencies?

• No
• Yes (please check binary size changes)

Checklist:

• [] Tests added/updated for bug fixes or new features
• [] Compatible with Windows/Linux/macOS

[semanticdiff-com]

Review changes with  

Changed Files

File	Status
crates/moonutil/src/compiler_flags.rs	77% smaller

[lynzrand]

Thanks for your PR!

We're sorry about the current condition of our codebase that made things unclear, but the implementation in this PR is a little off. The distinction of MSVC and GCC needs to be done at runtime instead of compile-time, so cfg! macros don't work here. You can check the following code for reference on how to detect MSVC while we're sorting things out.

moon/crates/moonbuild/src/gen/gen_build.rs

Lines 743 to 749 in b897b6d

	// note: this is a workaround for windows cl, x86_64-pc-windows-gnu also need to consider
	.args_with_cond(
	cfg!(target_os = "windows")
	&& moonc_opt.link_opt.target_backend == TargetBackend::LLVM
	&& CC::default().is_msvc(),
	["-llvm-target", "x86_64-pc-windows-msvc"],
	)

[CrazyboyQCD]

Thanks for your PR!

We're sorry about the current condition of our codebase that made things unclear, but the implementation in this PR is a little off. The distinction of MSVC and GCC needs to be done at runtime instead of compile-time, so cfg! macros don't work here. You can check the following code for reference on how to detect MSVC while we're sorting things out.

moon/crates/moonbuild/src/gen/gen_build.rs

Lines 743 to 749 in b897b6d

	// note: this is a workaround for windows cl, x86_64-pc-windows-gnu also need to consider
	.args_with_cond(
	cfg!(target_os = "windows")
	&& moonc_opt.link_opt.target_backend == TargetBackend::LLVM
	&& CC::default().is_msvc(),
	["-llvm-target", "x86_64-pc-windows-msvc"],
	)

I test that clang also fails to link m.lib, and as comment in #861 (comment) said, windows doesn't need this flag not just for msvc target.

[lynzrand]

Okay, I have just verified that both MSVC and GNU targets on Windows have math functions defined in MSVCRT. We will discuss this change internally before proceeding.

[lynzrand]

At the meantime, you might want to sign the CLA to make your changes mergable :)

Check this CI for more details: https://github.com/moonbitlang/moon/actions/runs/16511697077/job/46694762934?pr=944

[lynzrand]

Do note that if we're doing cross-compilation in the future, we can't use a compile-time cfg! as condition.