[gdb/testsuite] Fix info-var.exp for debug info from other files

[gdb/testsuite] Fix info-var.exp for debug info from other files

On openSUSE Leap 15.1, I get:
...
FAIL: gdb.base/info-var.exp: info variables
FAIL: gdb.base/info-var.exp: info variables -n
...
because the info variables command prints info also for init.c:
...
File init.c:^M
24:     const int _IO_stdin_used;^M
...
while the regexps in the test-case only expect info for info-var-f1.c and
info-var-f2.c.

Fix this by extending the regexps.

Tested on x86_64-linux, both openSUSE Leap 15.1 and Fedora 30.

gdb/testsuite/ChangeLog:

2019-08-28  Tom de Vries  <tdevries@suse.de>

	* gdb.base/info-var.exp: Allow info variables to print info for files
	other than info-var-f1.c and info-var-f2.c.