[llvm] [Windows] Avoid loading shared system libraries from user directory (PR #90520)

[via llvm-commits]

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@@ -43,6 +43,10 @@ InitLLVM::InitLLVM(int &Argc, const char **&Argv,
   assert(!Initialized && "InitLLVM was already initialized!");
   Initialized = true;
 #endif
+#ifdef _WIN32
+  // Avoid searching the directory from which the application is loaded.
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jofrn wrote:

> If removing the current directory from the search path is the desired behavior, then I'd recommend using `SetDefaultDllDirectories(LOAD_LIBRARY_SEARCH_DEFAULT_DIRS)` instead, since it's much easier to understand.

Reworked the commit to instead use `LoadLibraryExA(..., LOAD_LIBRARY_SEARCH_SYSTEM32)`. It seems `LOAD_LIBRARY_SEARCH_DEFAULT_DIRS` will search user directories, among other flags listed, which we should avoid since falling back to finding `dbghelp.dll` or `dbgcore.dll` here is still dangerous. There doesn't seem to be a flag to omit just the load directory.

https://github.com/llvm/llvm-project/pull/90520