libgo: adapt Solaris 12 references

With the change in the Solaris release model (no more major releases
like Solaris 12 but only minor ones like 11.4), the Solaris 12
references in GCC need to be adapted.

Patch by Rainer Orth.

Change-Id: Iab18a2525b461643ad9f661c0068287e85895326
Reviewed-on: https://go-review.googlesource.com/77490
Reviewed-by: Ian Lance Taylor <iant@golang.org>
5 files changed