[llvm] CMake: Force MSVC to read code as UTF-8

Symptoms: clangd/clangd#571

Reviewed By: kadircet

Differential Revision: https://reviews.llvm.org/D90116

Author: kirillbobyrev

llvm/CMakeLists.txt

@@ -599,6 +599,8 @@ if(MSVC)
   if (BUILD_SHARED_LIBS)
     message(FATAL_ERROR "BUILD_SHARED_LIBS options is not supported on Windows.")
   endif()
+  # Force MSVC to read code as UTF-8.
+  add_compile_options(/utf-8)
 else()
   option(LLVM_LINK_LLVM_DYLIB "Link tools against the libllvm dynamic library" OFF)
   option(LLVM_BUILD_LLVM_C_DYLIB "Build libllvm-c re-export library (Darwin only)" OFF)