binutils: use default ${CC} instead of defining it own

binutils.inc exports its own ${CC} which is similar to default ${CC}
but missing ${TOOLCHAIN_OPTION}, which makes --sysroot option lost
when compiling target binutils which then further breaks sstate.

Signed-off-by: Kevin Tian <kevin.tian@intel.com>

meta/recipes-devtools/binutils/binutils.inc

@@ -75,8 +75,6 @@ export CC_FOR_BUILD = "${BUILD_CC}"
 export CPP_FOR_BUILD = "${BUILD_CPP}"
 export CFLAGS_FOR_BUILD = "${BUILD_CFLAGS}"
 
-export CC = "${CCACHE}${HOST_PREFIX}gcc ${HOST_CC_ARCH}"
-
 do_configure () {
 	(cd ${S}; gnu-configize) || die "Failed to run gnu-configize"
 	oe_runconf