crossgcc: Always update HOSTCFLAGS from GMP headers if already built

Change-Id: I332cdec6d56cf09b0380dbf43575ed2d5d45461a
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/88232
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin L Roth <gaumless@gmail.com>

util/crossgcc/buildgcc

@@ -512,6 +512,10 @@ generic_build()
 
 	mkdir -p "$builddir"
 
+	if [ "$package" = "GMP" ] && [ -f "$DESTDIR$TARGETDIR/include/gmp.h" ]; then
+		set_hostcflags_from_gmp
+	fi
+
 	if [ -f "$success" ]; then
 		printf "Skipping $package v$version for $host_target as it is already built\n"
 	else