[compiler-rt] Test fixups for MSVC. (PR #109887)

[Martin Storsjö via llvm-commits]

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@@ -7,6 +7,9 @@
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
+#if _MSC_VER
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mstorsjo wrote:

`defined(_MSC_VER)`

https://github.com/llvm/llvm-project/pull/109887