Reviving SH FDPIC target

[Rich Felker <dalias@libc.org>]

I've started work on reviving the FDPIC support patch for the SH
target, which was proposed upstream in 2010 then abandoned:

https://gcc.gnu.org/ml/gcc-patches/2010-08/msg01464.html

Right now I'm in the process of determining what parts can be applied
as-is to current gcc, and what parts need to be adapted or rewritten
to account for changes in gcc between the 4.5 era and now (5.2/6.0).

The original patch as posted contained a significant amount of changes
that were unrelated to FDPIC code generation but rather for adding
sh*-uclinux tuples, and some things that even look like they're
associated with the old bFLT format. I am omitting these parts for now
since I'm unfamiliar with the old uClinux stuff and it's unmaintained.
If anyone else wants to use it, I think it would make more sense
factored as a separate patch anyway.

The target I have in mind is SH-2/J2 with musl libc, but uClibc or
even glibc could be made to work with it. I will submit the patches
for musl support (basically, just hooking up the dynamic linker name
for fdpic) separately; I believe they'll need merging with the
already-pending musl support patch from Szabolcs Nagy.

One question I'd like to ask now in case it's a problem that takes a
while to work out -- is copyright assignment already handled for the
old patch? The contributors listed in it are (all codesourcery):

- Daniel Jacobowitz
- Joseph Myers
- Mark Shinwell
- Andrew Stubbs

Also, according to Joseph Myers, there was some unresolved
disagreement that stalled (and eventually sunk) the old patch, so if
anyone's still around who has objections to it, could you speak up and
let me know what's wrong? Kaz Kojima seems to have approved the patch
at the time so I'm confused what the issue was/is.

Rich