Respect environment CPPFLAGS when we run ./configure so we can inject
random -D things without having to set CFLAGS/ASFLAGS

diff -durN glibc-2.13.orig/Makeconfig glibc-2.13/Makeconfig
--- glibc-2.13.orig/Makeconfig	2009-05-09 23:57:56.000000000 +0200
+++ glibc-2.13/Makeconfig	2009-11-13 00:49:41.000000000 +0100
@@ -697,6 +697,7 @@
 	   $(foreach lib,$(libof-$(basename $(@F))) \
 			 $(libof-$(<F)) $(libof-$(@F)),$(CPPFLAGS-$(lib))) \
 	   $(CPPFLAGS-$(<F)) $(CPPFLAGS-$(@F)) $(CPPFLAGS-$(basename $(@F)))
+CPPFLAGS += $(CPPFLAGS-config)
 override CFLAGS	= -std=gnu99 $(gnu89-inline-CFLAGS) \
 		  $(filter-out %frame-pointer,$(+cflags)) $(+gccwarn-c) \
 		  $(sysdep-CFLAGS) $(CFLAGS-$(suffix $@)) $(CFLAGS-$(<F)) \
