Subzero: Start writing out some relocation sections (text)

Start writing out some relocation sections (text).

Pass the full assembler pointer to the elf writer, so
that it has access to both the text buffer and the fixups.

Remove some child classes of AssemblerFixups. They didn't
really do much, and were pretty much identical to the
original AssemblerFixup class. Dart had a virtual method
for fixups to do necessary patching, but we currently
don't do the patching and just emit the relocations.
TODO see if patching is more efficient than writing out
relocations and letting the linker do the work.

This CL also makes AssemblerFixups POD.

Change the fixup kind to be a plain unsigned int, which
the target can fill w/ target/container-specific values.

Move the fwd declaration of Assembler to IceDefs and remove
the others. Do similar for fwd declaration refactoring for
ELFWriter.

Make the createAssembler method return a std::unique_ptr.

BUG=none
R=stichnot@chromium.org

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=ec27073120be04bf6234a0742e40ae3454ef9d3f

[jvoung (off chromium), 2015-01-12 19:32:56]

jvoung@chromium.org changed reviewers:
+ stichnot@chromium.org

[Jim Stichnoth, 2015-01-12 21:39:32]

otherwise lgtm

https://codereview.chromium.org/828873002/diff/120001/src/IceFixups.cpp
File src/IceFixups.cpp (right):

https://codereview.chromium.org/828873002/diff/120001/src/IceFixups.cpp#newco...
src/IceFixups.cpp:36: assert(llvm::isa<ConstantFloat>(C) ||
llvm::isa<ConstantDouble>(C));
This assert will probably eventually be incorrect, right?  Add a comment about
it?

https://codereview.chromium.org/828873002/diff/120001/src/IceFixups.h
File src/IceFixups.h (right):

https://codereview.chromium.org/828873002/diff/120001/src/IceFixups.h#newcode21
src/IceFixups.h:21: class ConstantRelocatable;
Is this forward declaration needed?

[jvoung (off chromium), 2015-01-12 22:41:28]

https://codereview.chromium.org/828873002/diff/120001/src/IceFixups.cpp
File src/IceFixups.cpp (right):

https://codereview.chromium.org/828873002/diff/120001/src/IceFixups.cpp#newco...
src/IceFixups.cpp:36: assert(llvm::isa<ConstantFloat>(C) ||
llvm::isa<ConstantDouble>(C));
On 2015/01/12 21:39:32, stichnot wrote:
> This assert will probably eventually be incorrect, right?  Add a comment about
> it?

Added a comment.

https://codereview.chromium.org/828873002/diff/120001/src/IceFixups.h
File src/IceFixups.h (right):

https://codereview.chromium.org/828873002/diff/120001/src/IceFixups.h#newcode21
src/IceFixups.h:21: class ConstantRelocatable;
On 2015/01/12 21:39:32, stichnot wrote:
> Is this forward declaration needed?

Oops no -- done.

[jvoung (off chromium), 2015-01-13 01:00:27]

Committed patchset #8 (id:70021) manually as
ec27073120be04bf6234a0742e40ae3454ef9d3f (presubmit successful).