Remove the MCSubtargetInfo argument from applyFixup, introduced in https://reviews.llvm.org/D45962 , as it's only required by ARM. Instead, add const MCFragment & so that ARMAsmBackend can retrieve MCSubtargetInfo via a static member function. Additionally, remove the MCAssembler argument, which is also only required by ARM. Additionally, make applyReloc non-const. Its arguments now fully cover addReloc's functionality.