[libc++] Mark libc++ deallocation helpers as noexcept (llvm#110884)

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 llvm#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);