Remove obsolete Solaris 10 support

[Ian Lance Taylor]

From: Rainer Orth <ro@cebitec.uni-bielefeld.de>
Date: Mon, May 13, 2019 at 4:39 AM

> With the GCC 9.1 release out of the door, this patch implements the
> removal of Solaris 10 support that had been obsoleted in GCC 9.

...

> The vast majority of the patch falls squarely under my Solaris
> maintainership.  I'm uncertain about the libbacktrace/configure.ac bit
> and will submit the libgo part separately.

The libbacktrace change looks fine to me.

Ian