convert gprof flags to style of rest of Makefile

Signed-off-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Message-Id: 
diff --git a/configure b/configure
index d371c69..6349d2e 100755
--- a/configure
+++ b/configure
@@ -2169,6 +2169,7 @@
   fi
   if test "$target_softmmu" = "yes" ; then
     ldflags="-p $ldflags"
+    echo "GPROF_CFLAGS=-p" >> $config_mak
   fi
 fi