Added elf in the link libraries.

It is unclear why the dependencies of libmumps did not take care of
this. Need to revisit the use of -lelf in the sr_linux directory.
Declaring force_32 and call_4lcldo_variant.

They were declared as extern, but the symbols where missing at link
time. We may as well declare them static here. This will need to be
revisited.
Adding elf library to gtcm_play executable.

To address undefined symbols.