[gdb/testsuite] Fix duplicate test-names in gdb.{gdb,opt,xml}

[gdb/testsuite] Fix duplicate test-names in gdb.{gdb,opt,xml}

There are 3 test directories with one duplicate test-name: gdb.gdb, gdb.opt
and gdb.xml.  The duplicates are:
...
DUPLICATE: gdb.gdb/complaints.exp: call complaint_internal ($cstr)
DUPLICATE: gdb.opt/inline-locals.exp: info locals above bar 2 \
  (PRMS: gdb/25695)
DUPLICATE: gdb.xml/tdesc-regs.exp: ptype $extrareg
...

Fix as appropriate.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2020-05-12  Tom de Vries  <tdevries@suse.de>

	* gdb.gdb/complaints.exp: Use with_test_prefix.
	* gdb.xml/tdesc-regs.exp: Same.
	* gdb.opt/inline-locals.exp: Fix test name.