[SystemZ] Update non-pic DWARF encodings

As pointed out by Rafael Espindola, we should match the DWARF encodings
produced by GCC in both pic and non-pic modes.  This was not the case
for the non-pic case.

This patch changes all DWARF encodings to DW_EH_PE_absptr for the
non-pic case, just like GCC does.  The test case is updated to check
for both variants.