[libc++][libunwind] Fixes to allow GCC 13 to compile libunwind/libc++abi/libc++

These are changes to allow GCC 13 to successfully compile the runtimes stack.

Reviewed By: ldionne, #libc, #libunwind, MaskRay

Spies: MaskRay, zibi, SeanP, power-llvm-team, mstorsjo, arichardson, libcxx-commits

Differential Revision: https://reviews.llvm.org/D151387

Author: philnik777

libcxx/include/__type_traits/remove_cv.h

@@ -19,7 +19,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if __has_builtin(__remove_cv)
+#if __has_builtin(__remove_cv) && !defined(_LIBCPP_COMPILER_GCC)
 template <class _Tp>
 struct remove_cv {
   using type _LIBCPP_NODEBUG = __remove_cv(_Tp);

libcxx/include/__type_traits/remove_cvref.h

@@ -20,7 +20,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if __has_builtin(__remove_cvref)
+#if __has_builtin(__remove_cvref) && !defined(_LIBCPP_COMPILER_GCC)
 template <class _Tp>
 using __remove_cvref_t _LIBCPP_NODEBUG = __remove_cvref(_Tp);
 #else

libunwind/src/CMakeLists.txt

@@ -80,11 +80,6 @@ endif()
 
 # Setup flags.
 add_link_flags_if(CXX_SUPPORTS_UNWINDLIB_EQ_NONE_FLAG --unwindlib=none)
-if (CXX_SUPPORTS_NOSTDLIBXX_FLAG)
-  add_link_flags_if_supported(-nostdlib++)
-else()
-  add_link_flags_if_supported(-nodefaultlibs)
-endif()
 
 # MINGW_LIBRARIES is defined in config-ix.cmake
 add_library_flags_if(MINGW "${MINGW_LIBRARIES}")