[libc++] Mark libc++ deallocation helpers as noexcept

They already can't throw exceptions and they are called from noexcept
functions, but they were not marked as noexcept. Depending on compiler
inlining, this might not make a difference or this might improve the
codegen a bit by removing the implicit try-catch block that Clang
generates around non-noexcept functions called from noexcept functions.

The original issue also mentioned that one occurrence of
std::allocator::deallocate was missing noexcept, however
it has since then been removed.

Fixes #66100

Author: ldionne

libcxx/include/new

@@ -281,7 +281,7 @@ _LIBCPP_HIDE_FROM_ABI void* __libcpp_operator_new(_Args... __args) {
 }
 
 template <class... _Args>
-_LIBCPP_HIDE_FROM_ABI void __libcpp_operator_delete(_Args... __args) {
+_LIBCPP_HIDE_FROM_ABI void __libcpp_operator_delete(_Args... __args) _NOEXCEPT {
 #if __has_builtin(__builtin_operator_new) && __has_builtin(__builtin_operator_delete)
   __builtin_operator_delete(__args...);
 #else
@@ -302,7 +302,7 @@ inline _LIBCPP_HIDE_FROM_ABI void* __libcpp_allocate(size_t __size, size_t __ali
 }
 
 template <class... _Args>
-_LIBCPP_HIDE_FROM_ABI void __do_deallocate_handle_size(void* __ptr, size_t __size, _Args... __args) {
+_LIBCPP_HIDE_FROM_ABI void __do_deallocate_handle_size(void* __ptr, size_t __size, _Args... __args) _NOEXCEPT {
 #if !_LIBCPP_HAS_SIZED_DEALLOCATION
   (void)__size;
   return std::__libcpp_operator_delete(__ptr, __args...);
@@ -311,7 +311,7 @@ _LIBCPP_HIDE_FROM_ABI void __do_deallocate_handle_size(void* __ptr, size_t __siz
 #endif
 }
 
-inline _LIBCPP_HIDE_FROM_ABI void __libcpp_deallocate(void* __ptr, size_t __size, size_t __align) {
+inline _LIBCPP_HIDE_FROM_ABI void __libcpp_deallocate(void* __ptr, size_t __size, size_t __align) _NOEXCEPT {
 #if !_LIBCPP_HAS_ALIGNED_ALLOCATION
   (void)__align;
   return __do_deallocate_handle_size(__ptr, __size);
@@ -325,7 +325,7 @@ inline _LIBCPP_HIDE_FROM_ABI void __libcpp_deallocate(void* __ptr, size_t __size
 #endif
 }
 
-inline _LIBCPP_HIDE_FROM_ABI void __libcpp_deallocate_unsized(void* __ptr, size_t __align) {
+inline _LIBCPP_HIDE_FROM_ABI void __libcpp_deallocate_unsized(void* __ptr, size_t __align) _NOEXCEPT {
 #if !_LIBCPP_HAS_ALIGNED_ALLOCATION
   (void)__align;
   return __libcpp_operator_delete(__ptr);