tools resolve_btfids: Always force HOSTARCH

Seth reported problem with cross builds, that fail
on resolve_btfids build, because we are trying to
build it on cross build arch.

Fixing this by always forcing the host arch.
Reported-by: NSeth Forshee <seth.forshee@canonical.com>
Signed-off-by: NJiri Olsa <jolsa@kernel.org>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NAndrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200923185735.3048198-2-jolsa@kernel.org

tools/bpf/resolve_btfids/Makefile

 # SPDX-License-Identifier: GPL-2.0-only
 include ../../scripts/Makefile.include
+include ../../scripts/Makefile.arch
 
 ifeq ($(srctree),)
 srctree := $(patsubst %/,%,$(dir $(CURDIR)))
@@ -29,6 +30,7 @@ endif
 AR       = $(HOSTAR)
 CC       = $(HOSTCC)
 LD       = $(HOSTLD)
+ARCH     = $(HOSTARCH)
 
 OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/