Clean up the diff -u test a little.



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@9279 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/configure.in b/configure.in
index ed8fd3f..a3dcd83 100644
--- a/configure.in
+++ b/configure.in
@@ -121,14 +121,16 @@
 
 # Comparing two identical files results in 0, unless -u isn't supported (as
 # it's not on AIX).
-touch tmp-xxx;
-if diff -u tmp-xxx tmp-xxx ; then
+tmpfile="tmp-xxx-yyy-zzz"
+touch $tmpfile;
+if diff -u $tmpfile $tmpfile ; then
     AC_MSG_RESULT([yes])
     DIFF="diff -u"
 else
     AC_MSG_RESULT([no])
     DIFF="diff"
 fi
+rm $tmpfile
 
 
 # We don't want gcc < 3.0