Add comment for the forked Dart revision for the assembler code.
Add comment for the forked Dart revision for the assembler code.

Also note to keep that up to date.
See also Patch set 1 of https://codereview.chromium.org/574133002/,
vs later patch sets.

Some things that were changed:
(*) Headers / constants use Ice version (RegX8632::Encoded_Reg_eax vs EAX), (KB / MB -> other...)
(*) Use llvm/Subzero allocator instead of Dart one.
(*) Class/Field/On-stack-replacement/Dart runtime stuff is removed
(*) Relocation/Fixups are now POD -- rather than a class
with a virtual method for fixup. For now, we write out
an ELF relocation, but later we may do a target pass
to handle function calls within the same section, etc.
(*) ASSERT -> assert
(*) uword -> uintptr_t (should check).
(*) clang-format
(*) ???

BUG=none
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/901453002

bkaradzic/SwiftShader,google/swiftshader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader