util/crossgcc/buildgcc: Allow bootstrapping CMake with multiple threads

The main build process already runs multi-threaded, when requested.
Apply the same setting to the bootstrap / configure step.

Change-Id: I89d6728a0985946b702f83770bedf767afb12690
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74156
Reviewed-by: Michael Niewöhner <foss@mniewoehner.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/crossgcc/buildgcc

@@ -893,6 +893,7 @@ 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