[clang] [C++20] [Modules] Introduce -fgen-reduced-bmi (PR #85050)

[Fangrui Song via cfe-commits]

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@@ -0,0 +1,53 @@
+// It is annoying to handle different slash direction
+// in Windows and Linux. So we disable the test on Windows
+// here.
+// REQUIRES: !system-windows
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MaskRay wrote:

UNSUPPORTED is much more common

https://github.com/llvm/llvm-project/pull/85050