Improve Solaris mudflap support (PR libmudflap/49550)

[Frank Ch. Eigler]

Hi, Rainer -

> >> >   If so, I'd rather do it by adding some MFWRAP_OS_SPEC to avoid
> >> >   having to duplicate the whole spec in the Solaris config
> >> >   headers.
> >
> > Why would solaris have to duplicate MFWRAP_SPEC if mmap64 is added to
> > the default gcc.c one?
> 
> I assumed that you wanted to keep the default generic, and meant to
> separate target specific additions from the generic part.

I don't have a strong opinion on this, but if you add mmap64 to the
default, there need be no target-specific additions for solaris, right?
So we can delay the decision to another day.

> [...]
> I could either commit the current version with the MFWRAP_SPEC addition
> and work from there, or wait until those failures are understood and
> fixed, too.

Committing now would be fine, assuming no regressions on a primary
platform.

- FChE