Rename *Options.td -> <flavor>Options.td.

Summary:
Before this patch, name of driver implementation is not consistent with its
option table file. Specifically, LDOptions has a different prefix than
GnuLdDriver.

This patch renames option files, so that the option files have the same prefix
as the corresponding driver files.

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1591