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

[Hans Wennborg via cfe-commits]

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@@ -135,6 +135,7 @@ endif()
 add_clang_library(libclang ${ENABLE_SHARED} ${ENABLE_STATIC} INSTALL_WITH_TOOLCHAIN
   OUTPUT_NAME ${output_name}
   ${SOURCES}
+  PARTIAL_SOURCES_INTENDED
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zmodem wrote:

As noted below, I think we should always include DllMain.cpp (on Windows), and then I think we don't need this?

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