arm/armasm: fix bug of plan9 register list argument

If the register list contains multiple sub-lists, e.g., [R0,R2-R3,R5-R7],
current implementation just flushes the last sub-list, i.e., [R5-R7].
The fix flushes previous sub-lists if any.

Fixes golang/go#19142

Change-Id: Ic4eaec76e4f654bf0b92b398b71b2050cede3cbb
Reviewed-on: https://go-review.googlesource.com/37172
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
2 files changed