[llvm] [CMake] Remove some always-true HAVE_XXX_H (PR #123087)

[Vlad Serebrennikov via llvm-commits]

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@@ -44,9 +44,7 @@
 #include <system_error>
 #include <vector>
 
-#ifdef HAVE_SYS_STAT_H
 #include <sys/stat.h>
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Endilll wrote:

Dropping `sys/stat.h` sounds good to me, but I'd wait for Fangrui to come online if time permits.

https://github.com/llvm/llvm-project/pull/123087