Unable to build with a clang/libcxx 21 system

[Muffindrake]

Every inclusion of the include/nihstro/shader_bytecode.h file throws this error:

/var/tmp/portage/dev-libs/nihstro-0_pre20250505/work/nihstro-f4d8659decbfe5d234f04134b5002b82dc515a44/include/nihstro/shader_bytecode.h:487:12: error: 'make_unsigned' cannot be specialized: Users are not allowed to specialize this standard library entity [-Winvalid-specialization]
  487 |     struct make_unsigned<nihstro::DestRegister> {
      |            ^
/usr/include/c++/v1/__type_traits/make_unsigned.h:75:8: note: marked '_Clang::no_specializations' here
   75 | struct _LIBCPP_NO_SPECIALIZATIONS make_unsigned {
      |        ^
/usr/include/c++/v1/__config:1167:9: note: expanded from macro '_LIBCPP_NO_SPECIALIZATIONS'
 1167 |       [[_Clang::__no_specializations__("Users are not allowed to specialize this standard library entity")]]
      |         ^

Which appears to be a recent-ish change to clang/libcxx ( llvm/llvm-project#101469 )

[Muffindrake]

Which of course can be worked around by explicitly passing -Wno-invalid-specialization, but does not fix the underlying problem.