tools build: Add HOSTARCH Makefile variable

tools build: Add HOSTARCH Makefile variable

For tools that needs to be always compiled with the host headers.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-907q32k2nep6q670dkxypmu6@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>