[gdb/testsuite] Fix FAILs due to PR gcc/101575

[gdb/testsuite] Fix FAILs due to PR gcc/101575

When running test-case gdb.ada/formatted_ref.exp with gcc-11 and target board
unix/gdb:debug_flags=-gdwarf-4 we run into:
...
(gdb) print/x s^M
No definition of "s" in current context.^M
(gdb) FAIL: gdb.ada/formatted_ref.exp: print/x s
...
which is caused by "runto defs.adb:20" taking us to defs__struct1IP:
...
(gdb) break defs.adb:20^M
Breakpoint 1 at 0x402cfd: defs.adb:20. (2 locations)^M
(gdb) run ^M
Starting program: formatted_ref ^M
^M
Breakpoint 1, defs__struct1IP () at defs.adb:20^M
20            return s.x;                   -- Set breakpoint marker here.^M
(gdb) print s1'access^M
...
instead of the expected defs.f1:
...
(gdb) break defs.adb:20^M
Breakpoint 1 at 0x402d0e: file defs.adb, line 20.^M
(gdb) run ^M
Starting program: formatted_ref ^M
^M
Breakpoint 1, defs.f1 (s=...) at defs.adb:20^M
20            return s.x;                   -- Set breakpoint marker here.^M
...

This is caused by incorrect line info due to gcc PR 101575 - "[gcc-11,
-gdwarf-4] Missing .file <n> directive causes invalid line info".

Fix this by when landing in defs__struct1IP:
- xfailing the runto, and
- issuing a continue to land in defs.f1.

Likewise in a few other test-cases.

Tested on x86_64-linux, with:
- system gcc.
- gcc-11 and target boards unix/gdb:debug_flags=-gdwarf-4 and
  unix/gdb:debug_flags=-gdwarf-5.

gdb/testsuite/ChangeLog:

2021-07-22  Tom de Vries  <tdevries@suse.de>

	* gdb.ada/formatted_ref.exp: Add xfail for PR gcc/101575.
	* gdb.ada/iwide.exp: Same.
	* gdb.ada/pkd_arr_elem.exp: Same.