gdb/fortran: Add test for module variables in 'info variables' output

gdb/fortran: Add test for module variables in 'info variables' output

Recent work from Tom Tromey to better handle variables with associated
copy relocations has fixed a Fortran issue where module variables
wouldn't show up in the output of 'info variables'.

This commit adds a test for this functionality to ensure it doesn't
get broken in the future.

gdb/testsuite/ChangeLog:

	* gdb.fortran/module.exp: Extend with 'info variables' test.

Change-Id: I7306b1d0a9a72947fd48ad7a03f49df774d6573b