mv r12l_to_gbrp1{2,6}le from lavc to pixfmt_conv

to be able to used also in different places

+ use compat/endian.h (POSIX) macros in BYTE_SWAP

.github/scripts/macOS/prepare.sh

@@ -31,6 +31,12 @@ echo "PKG_CONFIG_PATH=/usr/local/lib/pkgconfig" >> "$GITHUB_ENV"
 echo "/usr/local/opt/qt/bin" >> "$GITHUB_PATH"
 echo "DYLIBBUNDLER_FLAGS=$DYLIBBUNDLER_FLAGS" >> "$GITHUB_ENV"
 
+# TODO TOREMOVE allow gnu::always_inline - remove when no macOS <= 14 runner
+macos_major=$(sw_vers -productVersion | cut -d. -f1)
+if [ "$macos_major" -le 14 ]; then
+        echo "CFLAGS=-std=c2x" >> "$GITHUB_ENV"
+fi
+
 set -- \
         asciidoctor \
         autoconf \