tools build: Fix cross compile build

He Kuang the new fixdep tool breaks cross compiling. The reason is it
wouldn't get compiled under host arch, but under cross arch and failed
to run.

We need to add support for host side tools build, meanwhile disabling
fixdep usage for cross arch builds.
Reported-by: He Kuang <hekuang@huawei.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/20151013124358.GB9467@krava.brq.redhat.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/build/Makefile.include

 build := -f $(srctree)/tools/build/Makefile.build dir=. obj
 
+ifdef CROSS_COMPILE
+fixdep:
+else
 fixdep:
 	$(Q)$(MAKE) -C $(srctree)/tools/build fixdep
+endif
 
 .PHONY: fixdep