gas: Don't emit relocations for coff for BFD_RELOC_ARM_THUMB_MOVT

The object format doesn't support these relocations - only one
relocation is output for a movw/movt pair.

TBD: Check to make sure that the preceding instruction actually
is a matching movw instruction.
incomplete: bfd: Support more pe-coff arm relocations

These are mostly unfinished, but this is enough for assembling
in some setups at least.
not for review: bfd: coff-arm: hack: Don't adjust pcrel relocations

This is a huge hack - the right fix would probably be to
adjust md_pcrel_from_section in gas/config/tc-arm.c
to do the right thing, whatever that is.
not for review: gas: Hack pcrel base offsets for wince

This makes all the relocations end up right, at least in the
tested cases. Implications not yet understood.
gas: Silence a warning in the armv7-win config

This isn't directly related to armv7-win but more to assembling
manually written files, in contrary to gcc output.
Add a test case for the win-armv7 relocations
bfd: Update configure with the new target

This change should probably be autogenerated.