ARM: Support SingleParameterDotFile on WoA

Currently, the integrated assembler is the only choice for assembling Windows on
ARM binaries.  IAS supports the .file <filename> directive which emits the file
symbol into the resulting object binary.  Mark the GNU COFF information to
indicate support for this feature.
MC: style tweaks to WinCOFFStreamer

Stylistic changes to prepare for splitting up the COFFStreamer into target
specific streamers.  Tweak some assertion messages.  No functional change.
MC: rename WinCOFFStreamer and move declaration out-of-line

This is in preparation for promoting WinCOFFStreamer to a base class which will
be shared by the X86 and ARM specific target COFF streamers.  Also add a new
getOrCreateSymbolData interface (like MCELFStreamer) for the ARM COFF Streamer.
This makes the COFFStreamer more similar to the ELFStreamer.