Revert "Build libSupport with -Werror=global-constructors (NFC)"

This reverts commit 579cc9ad.
This breaks on Windows.

llvm/lib/Support/CMakeLists.txt

 include(GetLibraryName)
 
-# Ensure that libSupport does not carry any static global initializer.
-# libSupport can be embedded in use cases where we don't want to load all
-# cl::opt unless we want to parse the command line.
-# ManagedStatic can be used to enable lazy-initialization of globals.
-# We don't use `add_flag_if_supported` as instead of compiling an empty file we
-# check if the current platform is able to compile global std::mutex with this
-# flag (Linux can, Darwin can't for example).
-SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror=global-constructors")
-SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Werror=global-constructors")
-CHECK_CXX_SOURCE_COMPILES("
-  #include <mutex>
-  static std::mutex TestGlobalCtorDtor;
-  static std::recursive_mutex TestGlobalCtorDtor2;
-  int main() { (void)TestGlobalCtorDtor; (void)TestGlobalCtorDtor2; return 0;}
-  " LLVM_HAS_NOGLOBAL_CTOR_MUTEX)
-if (NOT LLVM_HAS_NOGLOBAL_CTOR_MUTEX)
-  string(REPLACE "-Werror=global-constructors" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
-  string(REPLACE "-Werror=global-constructors" "" CMAKE_CXX_FLAGS ${CMAKE_C_FLAGS})
-endif()
-
 if(LLVM_ENABLE_ZLIB)
   set(imported_libs ZLIB::ZLIB)
 endif()