Makefile: Move `--no-warn-rwx-segments' into xcompile

The parameter is not available for binutils older than 2.39. So move it
to xcompile to provide backwards compatibility for a bit.

Change-Id: I02982769ae2c356f037a747e85d155368bfcb730
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83693
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>

util/xcompile/xcompile

@@ -241,6 +241,12 @@ detect_special_flags() {
 	testcc "$GCC"      "$CFLAGS_GCC -Wextra" &&
 		CFLAGS_GCC="$CFLAGS_GCC -Wextra"
 
+	# Disable warning on segments with RWX.
+	# All loadable sections are placed in the same segment for simplicity.
+	testld "$GCC" "$FLAGS_GCC" "${GCCPREFIX}ld${LINKER_SUFFIX}" \
+		"$LDFLAGS --no-warn-rwx-segments" && \
+		LDFLAGS="$LDFLAGS --no-warn-rwx-segments"
+
 	case "$architecture" in
 	x86)
 		;;