Move krb5-config to new src/build-tools directory

In preparation for adding a bunch of pkg-config data files, move
krb5-config into a new source tree subdirectory containing tools we
provide as outputs to other build systems.
Install pkg-config data files

Add seven data files for pkg-config, corresponding to the five modules
supported by krb5-config.  For krb5 and krb5-gssapi, we also provide
mit- versions for callers desiring to distinguish between our
implementation and Heimdal's.

Based on a patch from Stef Walter <stefw@gnome.org>.

ticket: 7529 (new)