tools: include u-boot version of sha256.h

When building tools the u-boot specific sha256.h is required, but the
host version of sha256.h is used when present. This leads to build errors
on FreeBSD which does have a system sha256.h include. Like libfdt_env.h
explicitly include u-boot's sha256.h.

cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
Acked-by: Simon Glass <sjg@chromium.org>

tools/Makefile

@@ -190,6 +190,7 @@ endif # !LOGO_BMP
 # Define _GNU_SOURCE to obtain the getline prototype from stdio.h
 #
 HOST_EXTRACFLAGS += -include $(srctree)/include/libfdt_env.h \
+		-include $(srctree)/include/sha256.h \
 		$(patsubst -I%,-idirafter%, $(UBOOTINCLUDE)) \
 		-I$(srctree)/lib/libfdt \
 		-I$(srctree)/tools \