Honor CFLAGS.

Index: config/get_cc
--- config/get_cc.orig
+++ config/get_cc
@@ -89,7 +89,7 @@ if test -n "$__gnuc__"; then
   warn="-Wall"
   OPTFLAGS=-O3
   ASMINLINE=yes
-  OPTFLAGS="$OPTFLAGS $warn"
+  OPTFLAGS="$CFLAGS $warn"
   cmd="$CC $CFLAGS $extraflag -fno-strict-aliasing -o $exe gnu.c"
   . log_cmd
   if test -s $exe; then