README: add doc for how to supply user specific compiler flags to Kbuild

Probably not all users are aware of this possibility, thus add a
pointer to the README. Also add a useful example.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>

diff --git a/README b/README
index b53ea7dfe3f6d8201d75135ffd001e4f7c19a96a..b055ae7ef29c71ca65917f0f5858e58308fec419 100644 (file)
--- a/README
+++ b/README
@@ -3719,6 +3719,11 @@ this behavior and build U-Boot to some external directory:
 Note that the command line "O=" setting overrides the KBUILD_OUTPUT environment
 variable.
 
 Note that the command line "O=" setting overrides the KBUILD_OUTPUT environment
 variable.
 

+User specific CPPFLAGS, AFLAGS and CFLAGS can be passed to the compiler by
+setting the according environment variables KCPPFLAGS, KAFLAGS and KCFLAGS.
+For example to treat all compiler warnings as errors:
+
+       make KCFLAGS=-Werror

 
 Please be aware that the Makefiles assume you are using GNU make, so
 for instance on NetBSD you might need to use "gmake" instead of
 
 Please be aware that the Makefiles assume you are using GNU make, so
 for instance on NetBSD you might need to use "gmake" instead of