Solaris: Specify ARCHFLAGS in CFLAGS

Solaris: Specify ARCHFLAGS in CFLAGS

Various autoconf tests which use the C compiler may yield different
results depending on whether or not we are compiling for x86 or amd64
on Solaris (different libraries are available, structures may be
different, et al). So, set CFLAGS depending on which arch we are
targeting, so the autoconf results are more consistent with the actual
compilation during the build.

Change-Id: I99ddefaabc3bb2e80abe698366b348238d51408d
Reviewed-on: http://gerrit.openafs.org/5786
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>