arm, x86: port minor fixes from main repo

The most important change is exporting plan9Syntax as GoSyntax
for use by cmd/objdump.

Also make tests more forgiving of not having the necessary
binaries for external tests: skip the test rather than failing it.

Change-Id: I30aaa614618d370b1002e4247905cd982c5f5175
Reviewed-by: Ian Lance Taylor <>
10 files changed