afs: Never #define away afsd_dynamic_vcaches

afs: Never #define away afsd_dynamic_vcaches

Some versions of the Solaris Studio compiler on SPARC (at least 12.2
and possibly others, but not 12.3) get a little confused by code like
this:

    extern int foo;
    int
    somefunc(void) {
        if (0) return foo;
        return 0;
    }

When optimization is turned off, this results in an undefined symbol
reference to 'foo' (which is normal), but the resulting object file
lacks a relocation entry for the symbol 'foo', so the symbol remains
undefined after linking. In the OpenAFS tree, this occurs in
afs_daemons.c which references afs_vcount and afs_cacheStats in this
manner due to afsd_dynamic_vcaches being defined as '0' on Solaris.
The end result is that the libafs kernel module is not loadable, since
it complains about afs_vcount and afs_cacheStats being undefined, even
though the symbol definitions are also in the module.

While this is a bug in Solaris Studio and has since been fixed, it is
simple to work around this so we are usable with more compilers. If we
just always declare afsd_dynamic_vcaches as a regular variable, it
works around this issue and keeps the code a tiny bit simpler. So, do
that.

Reviewed-on: http://gerrit.openafs.org/6888
Tested-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit e5821239cde138f74f73bec1bd9a3880d08ac3df)

Change-Id: Id0f4b36d2b8d6a18f663ca6c95b78f773255fa78
Reviewed-on: http://gerrit.openafs.org/6908
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>