[llvm] Support: Do not check if a file exists before executing (PR #128821)

[Fangrui Song via llvm-commits]

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@@ -20,7 +20,7 @@
 ;; Test error messages when unable to execute the preprocessor.
 
 ; RUN: not llvm-windres --preprocessor intentionally-missing-executable %p/Inputs/empty.rc %t.res 2>&1 | FileCheck %s --check-prefix=CHECK4
-; CHECK4: llvm-rc: Preprocessing failed: Executable "intentionally-missing-executable" doesn't exist!
+; CHECK4: llvm-rc: Preprocessing failed: posix_spawn failed: No such file or directory
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MaskRay wrote:

The message could be different on z/OS. See the `-DMSG=%errc_ENOENT` pattern

https://github.com/llvm/llvm-project/pull/128821