[gdb/testsuite] Kfail gdb.cp/ambiguous.exp FAILs for PR26602

[gdb/testsuite] Kfail gdb.cp/ambiguous.exp FAILs for PR26602

Kfail these FAILs as caused by PR exp/26602:
...
FAIL: gdb.cp/ambiguous.exp: print x.x
FAIL: gdb.cp/ambiguous.exp: print n.x
FAIL: gdb.cp/ambiguous.exp: print j.x
FAIL: gdb.cp/ambiguous.exp: print jva1.x
FAIL: gdb.cp/ambiguous.exp: print jva2.x
FAIL: gdb.cp/ambiguous.exp: print (A1)j
FAIL: gdb.cp/ambiguous.exp: print (A1)jva1
...

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2020-09-11  Tom de Vries  <tdevries@suse.de>

	PR exp/26602
	* gdb.cp/ambiguous.exp: Add KFAILs for PR26602.