* lib/gdb.exp (gdb_file_cmd): Revert the return value to
previous simple convention. Use a global variable to store
information about what was found.
(gdb_run_cmd): Adapt to reverted return value.
* gdb.base/remote.exp: Adapt to reverted return value.
* gdb.gdb/complaints.exp: Likewise.
* gdb.gdb/observer.exp: Likewise.
* gdb.gdb/selftest.exp: Likewise.
* gdb.gdb/xfullpath.exp: Likewise.