build system: pass CFLAGS to link stage too (closes bug 1376)

diff --git a/Makefile b/Makefile
index c8ff5fb..60edff9 100644
--- a/Makefile
+++ b/Makefile
@@ -571,6 +571,7 @@
       cmd_busybox__ ?= $(srctree)/scripts/trylink \
       "$@" \
       "$(CC)" \
+      "$(CFLAGS)" \
       "$(LDFLAGS) $(EXTRA_LDFLAGS)" \
       "$(core-y)" \
       "$(libs-y)" \