CL 64793 removed the collect step, which took all
the generated .o files and merged them into a single _all.o.
Now the generated .o files all go directly into the final .a.

The only property of the _all.o approach that was lost
in CL 64793 was that before we could be sure that the
one name we used was "ar-compatible", that is, short
enough not to be truncated.

Now that the generated .o files are being kept directly,
this CL gives them guaranteed ar-compatible names.

This doesn't matter for nearly all uses today, but for some
future processing it might help not to lose the .o suffix
or not to end up with two identical entries with truncated
names.

I might not have bothered with this except that it's what's
leftover after syncing my own CL disabling _all.o
(necessary for reproducible builds on macOS) against
Ian's CL 64793, which landed first.

Change-Id: Ic86ed2a51432a5a4c58dc523e092a86d341f1997
Reviewed-on: https://go-review.googlesource.com/67250
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>