Check for 'usage' and 'Usage'.

Submitted by Tim Rice <tim@multitalents.net>.  His comment is:

I noticed "make report" didn't show the cc version on most of
my System V platforms. This patch corrects this.

util/selftest.pl

@@ -49,7 +49,7 @@ if (open(IN,"<Makefile")) {
 }
 
 $cversion=`$cc -v 2>&1`;
-$cversion=`$cc -V 2>&1` if $cversion =~ "usage";
+$cversion=`$cc -V 2>&1` if $cversion =~ "[Uu]sage";
 $cversion=`$cc -V |head -1` if $cversion =~ "Error";
 $cversion=`$cc --version` if $cversion eq "";
 $cversion =~ s/Reading specs.*\n//;