util: Add the AFS_STRINGIZE() macro

util: Add the AFS_STRINGIZE() macro

Add a macro to help with easily printing the value of #define'd
constants, called AFS_STRINGIZE(). For example:

    printf("The value of AFS_SYSCALL is: " AFS_STRINGIZE(AFS_SYSCALL) "\n");

Reviewed-on: https://gerrit.openafs.org/12893
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Ian Wienand <iwienand@redhat.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit f5794e029903db79f345f42582230a1fd0f7d823)

Change-Id: I33d14a62a04c0f79521ec253d51587952bf909a3
Reviewed-on: https://gerrit.openafs.org/13091
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>