scripts/faddr2line: extend usage on generic arch

When cross-compiling, fadd2line should use the binary tool used for the
target system, rather than that of the host.

Link: http://lkml.kernel.org/r/20171121092911.GA150711@sofia


Signed-off-by: Liu Changcheng <changcheng.liu@intel.com>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: NeilBrown <neilb@suse.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>