Bug 1046585 part 8 - Move X86Assembler.h and AssemblerBuffer.h into jit/. r=sunfish

--HG--
rename : js/src/assembler/assembler/AssemblerBuffer.h => js/src/jit/shared/AssemblerBuffer-x86-shared.h
rename : js/src/assembler/assembler/X86Assembler.h => js/src/jit/shared/BaseAssembler-x86-shared.h