build: break compiler flags out of $(CC)

Having more than the executable in $(CC) only leads to
trouble in a number of situations.

Change-Id: I7642ca4068b3a3bd5798219d74de9e0eb85bb4e5
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/5769
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

util/xcompile/xcompile

@@ -147,7 +147,8 @@ detect_special_flags() {
 report_arch_toolchain() {
 	cat <<EOF
 # elf${TWIDTH}-${TBFDARCH} toolchain (${GCCPREFIX}gcc)
-CC_${TARCH}:=${GCCPREFIX}gcc ${CFLAGS}
+CC_${TARCH}:=${GCCPREFIX}gcc
+CFLAGS_${TARCH}:=${CFLAGS}
 CPP_${TARCH}:=${GCCPREFIX}cpp
 AS_${TARCH}:=${GCCPREFIX}as ${ASFLAGS}
 LD_${TARCH}:=${GCCPREFIX}ld${LINKER_SUFFIX} ${LDFLAGS}