LU-17257 build: use pkg-config to find krb5 libdir

LU-17257 build: use pkg-config to find krb5 libdir

This patch fixes kerberos5.m4 to use pkg-config to
find krb5 libdir instead of looking for the krb5
libraries in a static list of path.

Lustre-change: https://review.whamcloud.com/53010
Lustre-commit: TBD (from 9cccb643173acf536f542103d47e4af7057c0ff9)

Test-Parameters: trivial kerberos=true testlist=sanity-krb5

Change-Id: Ia15812932942171b019f3e73034a78f9185c16ce
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53024
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Colin Faber <cfaber@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>