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

[Martin Storsjö via llvm-commits]

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@@ -27,8 +28,8 @@ extern "C" {
 __declspec(dllexport) void foo1() {}
 }
 #elif defined(DLL2)
-extern "C" {
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mstorsjo wrote:

Here you lost an `extern "C" {`, and end up with unbalanced parentheses.

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