Solaris: Be more flexible about compilers

Solaris: Be more flexible about compilers

OpenSolaris doesn't have its C compiler in /opt/SUNWspro/bin/cc,
but we still have to be careful to avoid gcc, as that can't
build the kernel module.

As a short term stop gap, add a PATH_PROG test which looks in
both /opt/SUNWspro/bin and /opt/SunStudioExpress/bin for cc.
We probably should look in more places, and in the long run,
we should probably be taking whatever autoconf gives us
(for userspace, at least)

Change-Id: Ie31cf1bf474650a081fc101a2aa40cfa6bd39423
Reviewed-on: http://gerrit.openafs.org/1020
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>