ignore explicit #warnings in compiler tests

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@5872 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

configure

@@ -214,7 +214,7 @@ add_extralibs(){
 }
 
 check_cmd(){
-    "$@" 2>&1 | tee -a $logfile | { ! grep -q .; }
+    "$@" 2>&1 | tee -a $logfile | { ! grep -E -q -v '#warning|^In file'; }
 }
 
 check_cc(){