surprises in xfail support

[Janis Johnson <janis187 at us dot ibm dot com>]

I've been immersing myself in .exp files in the GCC testsuite and in
DejaGnu and have noticed some things that surprised me.

1. dg-xfail-if looks at the target list but ignores the lists of
   options following the targets.  Several tests specify those options
   but I can't find any indication that they've ever been used.

   Is this supported somewhere, or was it at one time?

2. The xfail list on a dg-do command is only used for "run", never for
   keywords "assemble", "compile", "link", and "preprocess.  There are,
   however, several tests that specify an xfail list for those keywords.
   Has this ever worked?

3. dg-xfail-if has no effect on the execution results of a test, just
   on the compilation.  There are a few 'dg-do run' tests that use it,
   but apparently because they're expected to fail at compile time.

Meanwhile I've been putting together a test suite for the test framework
with combinations of dg-do, dg-require*, dg-xfail-if, and dg-warning and
friends, with and without some new functionality I'm playing with that
I'll submit if it looks useful and not too complicated.  Currently the
tests are meant to be run on powerpc with -m32 or -m64 and on i686,
because that's where I'm trying them.  Besides making sure the framework
doesn't break, they might be useful as examples of how to combine these
commands in a test.

My goals right now are to be able to skip tests that are not relevant
for some targets, where that determination can't be made just by
looking at a list of targets, and to have better control over xfail.

Janis