Enable module test

[vitaut]

The test for the fmt-module target needs to be fixed and reenabled.

[soumik15630m]

Hey @vitaut, I'm putting working on a PR to fix this

I have the CMake fix ready (linking the fmt target to fmt-module on the manual PCM path successfully resolves the missing implementation symbols at link time).

However, I'm hitting a snag while trying to re-enable the module tests. When compiling with GCC 14, if the test file mixes standard library includes (like <string_view> or the entirety of gtest) with import fmt;, the compiler completely chokes with thousands of redefinition errors (e.g., redefinition of template<class _Tp, class _Up> constexpr const bool std::is_same_v@fmt). This is due to a well-known GCC bug regarding global module fragment deduplication.

How would you prefer to handle the test coverage for this PR?

• Option A (Minimal Smoke Test): Create a clean module-test.cc that strictly uses import fmt; and fmt::print without any standard library includes. This bypasses the GCC bug, perfectly validates that the linking issue from libfmt-module.a build with g++15 on OSX generate unresolved symbols #4695 is fixed, and runs cleanly across MSVC, Clang, and GCC.
• Option B (Full Suite with GCC Guard): Restore the full test suite for the module target, but conditionally disable it in CMake when compiling with GCC until the compiler bug is resolved upstream.

Let me know which direction you'd prefer and I'll wrap up the PR!

[vitaut]

I think option B is better but note that @MathewBensonCode is already working on this in #4702.

[soumik15630m]

Yupp, i'm not opening the pr rn....i will wait somedays