libfdt: migrate include/libfdt_env.h to a wrapper

libfdt_env.h is supposed to provide system-dependent defines.

scripts/dtc/libfdt/libfdt_env.h from upstream DTC is suitable
for user-space, so we should use this for USE_HOSTCC case.

For compiling U-Boot, we need to override such system-dependent
defines, so use <linux/libfdt_env.h> imported from Linux.

<libfdt.h> selects a proper one.  Maybe, we should split header
inclusion completely, but I do not want too many patches at one.

I can rip off the include/libfdt_env.h from HOST_EXTRACFLAGS.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/Makefile b/tools/Makefile
index f8731e7..d3387fa 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -242,7 +242,7 @@
 # Define __KERNEL_STRICT_NAMES to prevent typedef overlaps
 # Define _GNU_SOURCE to obtain the getline prototype from stdio.h
 #
-HOST_EXTRACFLAGS += -include $(srctree)/include/libfdt_env.h \
+HOST_EXTRACFLAGS += -include $(srctree)/include/compiler.h \
 		$(patsubst -I%,-idirafter%, $(filter -I%, $(UBOOTINCLUDE))) \
 		-I$(srctree)/lib/libfdt \
 		-I$(srctree)/tools \