[binutils-gdb] Add test for fetching TLS from core file

[sergiodj+buildbot at sergiodj dot net]

*** TEST RESULTS FOR COMMIT 280ca31f4d608082e1b61cd0b6d90fdc3450b9f3 ***

Author: Djordje Todorovic <djordje.todorovic@rt-rk.com>
Branch: master
Commit: 280ca31f4d608082e1b61cd0b6d90fdc3450b9f3

Add test for fetching TLS from core file

A correct PID is needed by `libthread_db' library supplied with
glibc repository revisions before commit c579f48edba8 ("Remove
cached PID/TID in clone") or versions before 2.25 release for
GDB to fetch value of TLS variable from core file.  On MIPS
platforms it was omitted and fetching value of TLS variable was not
available.

This adds a new test in order to be sure if GDB on native platforms
can successfully fetch value of TLS variable.

gdb/testsuite:

	* gdb.threads/tls-core.c: New file.
	* gdb.threads/tls-core.exp: Likewise.