sparc64's most wanted ports fixes

So the following 4 ports are those blocking the most other ports from
becoming packages.

audio/openal 48
multimedia/libheif 169
www/webkitgtk4,webkitgtk41 139
x11/qt6/qtbase 634

https://cranky.work/sparc64/2025-04-23/audio/openal.log

undefined reference to `std::filesystem::__cxx11::path::_M_split_cmpts()'


https://cranky.work/sparc64/2025-04-23/multimedia/libheif.log

heif_enc.cc:(.text+0x2508): undefined reference to `std::filesystem::__cxx11::path::_M_split_cmpts()'
heif_enc.cc:(.text+0x25ec): undefined reference to `std::filesystem::__cxx11::path::has_root_directory() const'
heif_enc.cc:(.text+0x2b64): undefined reference to `std::filesystem::__cxx11::path::has_filename() const'


https://cranky.work/sparc64/2025-04-23/www/webkitgtk4,webkitgtk41.log

GCC 11.2 or newer is required to build WebKit. Use a newer GCC version
or Clang

Looks like perhaps shifting to ports-clang may help here


https://cranky.work/sparc64/2025-04-23/x11/qt6/qtbase.log

Looks like this may have hidden dependencies and/or problems with cmake
finding necessary modules.


Help fixing these ports will increase the number of packages sparc64
has.

--Kurt