do not add NGX_GCC_OPT twice: it is added later with -W

auto/cc/gcc

diff --git a/auto/cc/gcc b/auto/cc/gcc
index e02d649..8ea1f58 100644
--- a/auto/cc/gcc
+++ b/auto/cc/gcc
@@ -51,8 +51,6 @@
 #NGX_GCC_OPT="-Os"
 NGX_GCC_OPT="-O"
 
-CFLAGS="$CFLAGS $NGX_GCC_OPT"
-
 #CFLAGS="$CFLAGS -fomit-frame-pointer"
 
 case $CPU in