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

This reverts commit 4d81c8a.

Apparently, we have code that indirectly uses #pragma
execution_character_set which depends on utf-8 not being set:

http://lab.llvm.org:8011/#/builders/127/builds/1161/steps/4/logs/stdio

Author: kirillbobyrev

llvm/CMakeLists.txt

@@ -599,8 +599,6 @@ 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)