Fix PR gdb/844

	Fix PR gdb/844
	* lib/gdb.exp (gdb_compile): Handle "quiet" option.
	(gdb_compile_pthreads): Pass "quiet" to gdb_compile.

	* gdb.threads/gcore-thread.exp: Use gdb_compile_pthreads.  Return
	instead of calling gdb_suppress_entire_file.
	* gdb.threads/print-threads.exp: Likewise.
	* gdb.threads/schedlock.exp: Likewise.

	* gdb.threads/killed.exp: Return instead of calling
	gdb_suppress_entire_file.
	* gdb.threads/linux-dp.exp: Likewise.
	* gdb.threads/pthreads.exp: Likewise.