autoconf: Combine the sparc/solaris configurations

According to cc's man page:

  v9        Is equivalent to -m64 -xarch=sparc
	    Legacy makefiles and scripts that use
	    -xarch=v9 to obtain the 64-bit memory model
	    need only use -m64.

Change-Id: Idd1021f3fef9c427072079f3c7d7aa9ca6fa0060
Reviewed-on: http://gerrit.openafs.org/10462
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Hutzelman <jhutz@cmu.edu>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>