[v636] Fix mac-beta builds after the latest update

[devajithvs]

Backport __builtin_clzg implementation in Clang: llvm/llvm-project@c1c2551a2876f.

This along with the other backports fixes mac-beta build on v6.36.

TODO: Add new llvm tag.

This Pull request:

Changes or fixes:

Checklist:

• tested changes locally
• updated the docs (if necessary)

This PR fixes #

[github-actions]

Test Results

    16 files      16 suites   2d 10h 19m 59s ⏱️
 2 747 tests  2 745 ✅ 0 💤 2 ❌
42 454 runs  42 452 ✅ 0 💤 2 ❌

For more details on these failures, see this check.

Results for commit 45b6e9b.

♻️ This comment has been updated with latest results.

[hahnjo]

Next errors when building std:

  While building module 'Core':
  While building module 'std' imported from input_line_1:1:
  In file included from <module-includes>:32:
  In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/type_traits:487:
  /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__type_traits/is_convertible.h:32:99: error: '_Tp' does not refer to a value
  struct _LIBCPP_NO_SPECIALIZATIONS is_nothrow_convertible : bool_constant<__is_nothrow_convertible(_Tp, _Up)> {};
                                                                                                    ^
  /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__type_traits/is_convertible.h:31:17: note: declared here
  template <class _Tp, class _Up>
                  ^
  /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__type_traits/is_convertible.h:32:104: error: '_Up' does not refer to a value
  struct _LIBCPP_NO_SPECIALIZATIONS is_nothrow_convertible : bool_constant<__is_nothrow_convertible(_Tp, _Up)> {};
                                                                                                         ^
  /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__type_traits/is_convertible.h:31:28: note: declared here
  template <class _Tp, class _Up>
                             ^
  /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__type_traits/is_convertible.h:35:102: error: '_Tp' does not refer to a value
  _LIBCPP_NO_SPECIALIZATIONS inline constexpr bool is_nothrow_convertible_v = __is_nothrow_convertible(_Tp, _Up);
                                                                                                       ^
  /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__type_traits/is_convertible.h:34:17: note: declared here
  template <class _Tp, class _Up>
                  ^
  /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__type_traits/is_convertible.h:35:107: error: '_Up' does not refer to a value
  _LIBCPP_NO_SPECIALIZATIONS inline constexpr bool is_nothrow_convertible_v = __is_nothrow_convertible(_Tp, _Up);
                                                                                                            ^
  /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__type_traits/is_convertible.h:34:28: note: declared here
  template <class _Tp, class _Up>
                             ^

and

  While building module 'Core':
  While building module 'std' imported from input_line_1:1:
  In file included from <module-includes>:156:
  In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/algorithm:1850:
  In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__algorithm/count.h:16:
  /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__bit/popcount.h:27:10: error: use of undeclared identifier '__builtin_popcountg'
    return __builtin_popcountg(__t);
           ^
  /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__stop_token/atomic_unique_lock.h:31:22: note: in instantiation of function template specialization 'std::__popcount<unsigned long long>' requested here
    static_assert(std::__popcount(static_cast<unsigned long long>(_LockedBit)) == 1,
                       ^
  /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__stop_token/atomic_unique_lock.h:31:17: error: static assertion expression is not an integral constant expression
    static_assert(std::__popcount(static_cast<unsigned long long>(_LockedBit)) == 1,
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~