x11/xdg-desktop-portal-hyprland: unbreak build after e602fc540b59

meson.build:1:0: ERROR: Unable to detect linker for compiler c++ -Wl,--version -fstack-protector-strong -O2 -pipe -fstack-protector-strong -fno-strict-aliasing -fexperimental-library -nostdinc++ -isystem/wrkdirs/usr/ports/x11/xdg-desktop-portal-hyprland/work-qt5/libcxx_prefix/include/c++/v1
stdout:
stderr: c++: error: unknown argument: '-fexperimental-library'

Reported by: pkg-fallout
(direct commit to 2023Q3 as 4df0e66a3662 is missing on the branch)