Handle TLS variable lookups when using separate debug files.

Handle TLS variable lookups when using separate debug files.

Commit df22c1e5d53c38f38bce6072bb46de240f9e0e2b handled the case that
a separate debug file was passed as the objfile for a shared library
to svr4_fetch_objfile_link_map.  However, a separate debug file can
also be passed for TLS variables in the main executable.  In addition,
frv_fetch_objfile_link_map also expects to be passed the original
objfile rather than a separate debug file, so pull the code to resolve
a separate debug file to the main objfile up into
target_translate_tls_address.