C++: dlsym casts in gdb/linux-thread-db.c and gdb/gdbserver/thread-db.c

C++: dlsym casts in gdb/linux-thread-db.c and gdb/gdbserver/thread-db.c

Implicit void * -> function pointer conversion doesn't work in C++, so
in C++, we need to cast the result of dlsym.  This adds a few typedefs
and macros that make this easy.  GDBserver's version already had the
CHK macro, so I added it to GDB too.

Tested on x86_64 Fedora 20, native and gdbserver.

gdb/gdbserver/ChangeLog:
2015-08-04  Pedro Alves  <palves@redhat.com>

	* thread-db.c (struct thread_db): Use new typedefs.
	(try_thread_db_load_1): Define local TDB_DLSYM macro and use it in
	CHK calls.
	(disable_thread_event_reporting): Cast result of dlsym to
	destination function pointer type.
	(thread_db_mourn): Use td_ta_delete_ftype.

gdb/ChangeLog:
2015-08-04  Pedro Alves  <palves@redhat.com>

	* nat/gdb_thread_db.h (td_init_ftype, td_ta_new_ftype)
	(td_ta_map_lwp2thr_ftype, td_ta_thr_iter_ftype)
	(td_ta_event_addr_ftype, td_ta_set_event_ftype)
	(td_ta_clear_event_ftype, td_ta_event_getmsg_ftype)
	(td_thr_validate_ftype, td_thr_get_info_ftype)
	(td_thr_event_enable_ftype, td_thr_tls_get_addr_ftype)
	(td_thr_tlsbase_ftype, td_symbol_list_ftype, td_ta_delete_ftype):
	New typedefs.
	* linux-thread-db.c (struct thread_db_info): Use new typedefs.
	(try_thread_db_load_1): Define TDB_VERBOSE_DLSYM, TDB_DLSYM , CHK
	local macros and use them instead of verbose_dlsym and dlsym
	calls.