scripts/gcc.sh: fix bashisms

voodoo@hestia:/opt/github/stable-kernel$ ./checkbashisms scripts/gcc.sh
script scripts/gcc.sh does not appear to be a /bin/sh script
possible bashism in scripts/gcc.sh line 26 (should be '.', not 'source'):
source ${DIR}/system.sh
possible bashism in scripts/gcc.sh line 33 (should be 'b = a'):
                if [ "x${distro}" == "xUbuntu" ] ; then
possible bashism in scripts/gcc.sh line 93 (should be 'b = a'):
        if [ "x${ARCH}" == "xarmv7l" ] ; then
possible bashism in scripts/gcc.sh line 133 (should be 'b = a'):
if [ "x${CC}" == "x" ] && [ "x${ARCH}" != "xarmv7l" ] ; then
possible bashism in scripts/gcc.sh line 135 (should be 'b = a'):
        if [ "x${CC}" == "x" ] ; then
possible bashism in scripts/gcc.sh line 142 (should be 'b = a'):
if [ "x${GCC_TEST}" == "x" ] ; then

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>
gcc: missed one bashism

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>