crossgcc/buildgcc: Remove invalid option for CMake

"--parallel" is not a valid option for CMake.

Change-Id: Idba76ce6a29e5d582ce49aa91ce4013aebc6d835
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/88230
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin L Roth <gaumless@gmail.com>

util/crossgcc/buildgcc

@@ -941,7 +941,6 @@ build_LLVM() {
 build_CMAKE() {
 	CC="$(hostcc host)" CXX="$(hostcxx host)" CFLAGS="$HOSTCFLAGS" \
 	../${CMAKE_DIR}/configure \
-		--parallel=${THREADS} \
 		--prefix="$TARGETDIR" || touch .failed
 	# shellcheck disable=SC2086
 	$MAKE $JOBS || touch .failed