- add CONFIG_EXTRA_CFLAGS (thanks to keesj)

This helps with remembering additional flags like e.g. cpu settings for
  people who did not configured their compiler to produce code for their cpu
  per default.

Config.in

@@ -411,6 +411,12 @@ config CROSS_COMPILER_PREFIX
 
 	  Native builds leave this empty.
 
+config EXTRA_CFLAGS
+	string "Additional CFLAGS"
+	default ""
+	help
+	  Additional CFLAGS to pass to the compiler verbatim.
+
 endmenu
 
 menu 'Debugging Options'

Makefile.flags

@@ -81,6 +81,11 @@ CFLAGS_busybox += $(ARCH_PIE)
 CFLAGS += $(ARCH_FPIE)
 endif
 
+ifneq ($(CONFIG_EXTRA_CFLAGS),)
+CFLAGS += $(strip $(subst ",,$(CONFIG_EXTRA_CFLAGS)))
+#"))
+endif
+
 LDLIBS += m crypt
 
 ifeq ($(CONFIG_PAM),y)