kbuild: fix buglet in gcc-version.sh

Greg Schafer <gschafer@zip.com.au> reported:
====
$make mrproper
scripts/gcc-version.sh: [[: command not found

This is on a very old host with an ancient bash as /bin/sh. But I have
CONFIG_SHELL set and pointing to a modern bash. Something is wrong.

This doesn't happen with 2.6.23
====

Fixed using a more common string equality test.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Greg Schafer <gschafer@zip.com.au>
Cc: Jesper Juhl <jesper.juhl@gmail.com>

scripts/gcc-version.sh

@@ -9,7 +9,10 @@
 # gcc-2.95.3, `030301' for gcc-3.3.1, etc.
 #
 
-if [[ $1 = "-p" ]] ; then with_patchlevel=1; shift; fi
+if [ "$1" = "-p" ] ; then
+	with_patchlevel=1;
+	shift;
+fi
 
 compiler="$*"