Fix LT_LDLIB_shlib_missing

Fix LT_LDLIB_shlib_missing

Libtool's -symbols-file argument is taken as an exact match of symbols
that this library claims to export.  It does not filter based on what
symbols are actually present in the objects comprising the library.
Instead, if there are symbols in the file which are not implemented
by the library, there is an implicit assumption that some other library
will provide those symbols, which must be linked into a consumer of
this library alongside this library.

These are not the semantics we want (at present, only for roken), wherein
a library will implement some (but probably not all) of a given list
of symbols, and we want the export list to reflect only those symbols
which are implemented.  Instead, use the symbols file to build a regex that
will only match symbols listed in the file (and no other symbols), and
only export the subset which is present.

Change-Id: Id81f7a35089ae7f760fe643680f9bfb9c81521aa
Reviewed-on: http://gerrit.openafs.org/11475
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: D Brashear <shadow@your-file-system.com>
Tested-by: D Brashear <shadow@your-file-system.com>