gdb/testsuite: spring clean the gdb.stabs/gdb11479.exp test

gdb/testsuite: spring clean the gdb.stabs/gdb11479.exp test

I had reason to look at the gdb.stabs/gdb11479.exp test script and
figured it could do with a small clean up.  I've:

  - Made use of standard_testfile and the variables it defines.

  - Made use of with_test_prefix and removed the prefix from the end
    of each test name.

  - Avoid overwriting the test binary when we recompile, instead use a
    different name for each recompilation.

  - Add '.' at the end of each comment.

There should be no changes in what is tested with this commit.

Reviewed-By: Keith Seitz <keiths@redhat.com>