perf tools: Version incorrect with some versions of grep

Some versions of grep don't treat '\s' properly. When building perf on such
systems and using a kernel tarball the perf version is unable to be determined
from the main kernel Makefile and the user is left with a version of '..'.
Replacing the use of '\s' with '[[:space:]]', which should work in all grep
versions, gives a usable version number.
Reported-by: Tapan Dhimant <tdhimant@akamai.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Tapan Dhimant <tdhimant@akamai.com>
Cc: linux-kernel@vger.kernel.org
Cc: stable@kernel.org
LKML-Reference: <1300241800-30281-1-git-send-email-johunt@akamai.com>
Signed-off-by: Josh Hunt <johunt@akamai.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/PERF-VERSION-GEN

@@ -23,10 +23,10 @@ if test -d ../../.git -o -f ../../.git &&
 then
 	VN=$(echo "$VN" | sed -e 's/-/./g');
 else
-	eval `grep '^VERSION\s*=' ../../Makefile|tr -d ' '`
-	eval `grep '^PATCHLEVEL\s*=' ../../Makefile|tr -d ' '`
-	eval `grep '^SUBLEVEL\s*=' ../../Makefile|tr -d ' '`
-	eval `grep '^EXTRAVERSION\s*=' ../../Makefile|tr -d ' '`
+	eval $(grep '^VERSION[[:space:]]*=' ../../Makefile|tr -d ' ')
+	eval $(grep '^PATCHLEVEL[[:space:]]*=' ../../Makefile|tr -d ' ')
+	eval $(grep '^SUBLEVEL[[:space:]]*=' ../../Makefile|tr -d ' ')
+	eval $(grep '^EXTRAVERSION[[:space:]]*=' ../../Makefile|tr -d ' ')
 
 	VN="${VERSION}.${PATCHLEVEL}.${SUBLEVEL}${EXTRAVERSION}"
 fi