Pass user defines for Barebox build

[Lior Weintraub]

Hi guys,

Is there a formal way to pass user compilation flags into Barebox build?
I couldn't find one so I just patched the main Makefile 
diff --git a/Makefile b/Makefile
index 471bbc2679..febc94b7f3 100644
--- a/Makefile
+++ b/Makefile
@@ -443,7 +443,7 @@ KBUILD_CPPFLAGS        := -D__KERNEL__ -D__BAREBOX__ $(LINUXINCLUDE) -fno-builti
 KBUILD_CFLAGS   := -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs \
                   -fno-strict-aliasing -fno-common -fshort-wchar \
                    -Werror=implicit-function-declaration -Werror=implicit-int \
-                   -Os -pipe -Wmissing-prototypes -std=gnu89
+                   -Os -pipe -Wmissing-prototypes -std=gnu89 $(BAREBOX_USER_CFLAGS)
 KBUILD_AFLAGS          := -D__ASSEMBLY__
 KBUILD_AFLAGS_KERNEL :=
 KBUILD_CFLAGS_KERNEL :=

This patch allowed me to set BAREBOX_CFLAGS environment when calling make.

Thanks,                         
Lior.