[gdb/testsuite] Fix gdb.gdb/python-helper.exp with -O2 -flto=auto and gcc 7.5.0 some...

[gdb/testsuite] Fix gdb.gdb/python-helper.exp with -O2 -flto=auto and gcc 7.5.0 some more

With a gdb build with -O2 -flto=auto and gcc 7.5.0 and test-case
gdb.gdb/python-helper.exp I run into:
...
(outer-gdb) continue^M
Continuing.^M
print 1^M
^M
Thread 1 "xgdb" hit Breakpoint 2, \
  _Z11value_printP5valueP7ui_filePK19value_print_options (val=0x22e2590, \
  stream=0x1f65480, options=0x7fffffffcdc0) at gdb/valprint.c:1193^M
1193    {^M
(outer-gdb) FAIL: gdb.gdb/python-helper.exp: hit breakpoint in outer gdb
...

This is the "value_print" variant of the problem with "c_print_type" I fixed
in commit 0d332f11122 ("[gdb/testsuite] Fix gdb.gdb/python-helper.exp with -O2
 -flto=auto and gcc 7.5.0").

Fix this likewise.

Tested on x86_64-linux.