x11/hypridle: unbreak build with libc++ 16

In file included from src/config/ConfigManager.cpp:1:
In file included from src/config/ConfigManager.hpp:3:
src/config/../helpers/Log.hpp:56:27: error: no member named 'vformat' in namespace 'std'
        std::cout << std::vformat(fmt, std::make_format_args(args...)) << "\n";
                     ~~~~~^
src/config/../helpers/Log.hpp:56:45: error: no member named 'make_format_args' in namespace 'std'
        std::cout << std::vformat(fmt, std::make_format_args(args...)) << "\n";
                                       ~~~~~^

Reported by:	pkg-fallout

x11/hypridle/Makefile

@@ -25,6 +25,12 @@ GH_ACCOUNT=	hyprwm
 LDFLAGS+=	-Wl,--as-needed # sdbus-cpp deps
 PLIST_FILES=	bin/${PORTNAME}
 
+# XXX Drop after FreeBSD 14.0 EOL around 2025-03-01
+.if exists(/usr/include/c++/v1/__format/format_functions.h) && \
+   !exists(/usr/include/c++/v1/__format/write_escaped.h)
+CXXFLAGS+=	-fexperimental-library
+.endif
+
 post-patch:
 # https://github.com/ConsoleKit2/ConsoleKit2/issues/150
 # https://github.com/ConsoleKit2/ConsoleKit2/issues/151