libpam.a fails to load any modules and does not work at all.
At the moment, openpam_load.c at least must be compiled with and without
OPENPAM_STATIC_MODULES for static and shared libraries, respectively.
Therefore, use CSHLIBFLAGS again, in order to build objects for static and
shared libraries separately.
This may be ugly, but seems better for me than adding further hacks in
libpam/libpam/Makefile, which is already complicated enough...
6ce10d32d6