use lazy evaluation for TARGET_CONFIGURE_OPTS to make it possible to override...

use lazy evaluation for TARGET_CONFIGURE_OPTS to make it possible to override TARGET_CC and TARGET_CXX

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@20566 3c298f89-4303-0410-b956-a3cf2f4a3e73

rules.mk

@@ -172,7 +172,7 @@ ifneq ($(CONFIG_CCACHE),)
   TARGET_CC:= ccache $(TARGET_CC)
 endif
 
-TARGET_CONFIGURE_OPTS:= \
+TARGET_CONFIGURE_OPTS = \
   AR=$(TARGET_CROSS)ar \
   AS="$(TARGET_CC) -c $(TARGET_CFLAGS)" \
   LD=$(TARGET_CROSS)ld \