In gdb_file_cmd, perror is called with error message strings using $arg and
$GDB, both of which contain path names, which makes comparison of gdb.sum
files more difficult.
Fix this by using:
- [file tail $arg] instead of $arg
- GDB instead of $GDB.
Tested on x86_64-linux.
gdb/testsuite/ChangeLog:
2020-06-04 Tom de Vries <tdevries@suse.de>
* lib/gdb.exp (gdb_file_cmd): Avoid path names in error messages.
