MC: introduce ability to restrict recorded relocations

Add support to allow a target specific COFF object writer to restrict the
recorded resolutions in the emitted object files.  This is motivated by the need
in Windows on ARM, where an intermediate relocation needs to be prevented from
being emitted in the object file.
MC: correct IMAGE_REL_ARM_MOV32T relocation emission

This corrects the emission of IMAGE_REL_ARM_MOV32T relocations.  Previously, we
were avoiding the high portion of the relocation too early.  If there was a
section-relative relocation with an offset greater than 16-bits (65535), you
would end up truncating the high order bits of the offset.  Allow the current
relocation representation to flow through out the MC layer to the object writer.
Use the new ability to restrict recorded relocations to avoid emitting the
relocation into the final object.