[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
+// On AIX, the default output for `-c` may be `.s` instead of `.o`,
+// which makes the test fail. So disable the test on AIX.
+// REQUIRES: !system-aix
+//
+// RUN: rm -rf %t
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MaskRay wrote:

redundant `mkdir`

`// RUN: rm -rf %t && split-file %s %t && cd %t`

If Windows backslashes feel annoying, you can add a `cd %t`

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