mv ext_CFLAGS on the end for overwriting existing CFLAGS

configure.ac

@@ -205,17 +205,17 @@ dnl the above AC_PROG_CC may set CFLAGS to "-O2 -g"
 if test "$enable_debug" = "no"; then
 	if test "x$GCC" = "xyes"; then
 		AC_MSG_WARN([Removing debugging option!])
-		CFLAGS="$ext_CFLAGS -O2 -Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes -Wnested-externs -Wold-style-definition -Wredundant-decls -Wconversion -s"
+		CFLAGS="-O2 -Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes -Wnested-externs -Wold-style-definition -Wredundant-decls -Wconversion -s $ext_CFLAGS"
 	else
 		AC_MSG_WARN([Removing debugging option!])
-		CFLAGS="$ext_CFLAGS -O2"
+		CFLAGS="-O2 $ext_CFLAGS"
 	fi
 else
     AC_DEFINE([NGDEBUG], [1], [Compile with debug info])
 	if test "x$GCC" = "xyes"; then
-		CFLAGS="$ext_CFLAGS -g -O1 -Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes -Wnested-externs -Wold-style-definition -Wredundant-decls -Wconversion"
+		CFLAGS="-g -O1 -Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes -Wnested-externs -Wold-style-definition -Wredundant-decls -Wconversion $ext_CFLAGS"
 	else
-		CFLAGS="$ext_CFLAGS -g"
+		CFLAGS="-g $ext_CFLAGS"
 	fi
 fi