[gdb/testsuite] Add gcc/94469 xfails to gdb.ada/call_pn.exp

[gdb/testsuite] Add gcc/94469 xfails to gdb.ada/call_pn.exp

When running test-case gdb.ada/call_pn.exp with target board
unix/-flto/-O0/-flto-partition=none/-ffat-lto-objects, we run into:
...
(gdb) print last_node_id^M
Multiple matches for last_node_id^M
[0] cancel^M
[1] pck.last_node_id at gdb/testsuite/gdb.ada/call_pn/pck.adb:17^M
[2] pck.last_node_id at gdb/testsuite/gdb.ada/call_pn/foo.adb:17^M
> FAIL: gdb.ada/call_pn.exp: print last_node_id after calling pn (timeout)
...

This failure is due to a gcc bug that declares two instead of one symbols,
filed as PR gcc/94469.

Add an xfail at this test.  Also add a similar xfail at an earlier test, that
only triggers with -readnow.  Stabilize test results by making sure the
earlier xfail is always triggered, using "maint expand-symtabs".

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2020-04-08  Tom de Vries  <tdevries@suse.de>

	PR testsuite/25760
	* gdb.ada/call_pn.exp: Call "maint expand-symtabs".  Add xfails.