[clang] Add DllMain entry point to `libclang.dll` (PR #171465)

[via cfe-commits]

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@@ -168,6 +169,9 @@ if(ENABLE_SHARED)
       # If llvm/libclang-cpp dll is also being built for windows clang c++ symbols will still be
       # implicitly be exported from libclang.
       target_compile_definitions(libclang PRIVATE CLANG_BUILD_STATIC)
+      if(LLVM_ENABLE_RPMALLOC)
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GkvJwa wrote:

Currently, the allocator lacks global macro definitions; adding them might introduce more pollution.

https://github.com/llvm/llvm-project/pull/171465