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

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.

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.
+add_flag_if_supported("-Werror=global-constructors" WERROR_GLOBAL_CONSTRUCTOR)
+
 if(LLVM_ENABLE_ZLIB)
   set(imported_libs ZLIB::ZLIB)
 endif()