By adding MachineType to LinkageLocation, it is possible not only to reason
about the location of a LinkageLocation on the stack, but also about it's
size. This will be useful in follow-on CLs that attempt to merge some of the
parameter passing logic of tail calls and normal (non-tail) calls.

As a nice side-effect, it is no longer necessary to separately keep a
MachineSignature in a CallDescriptor, because the MachineTypes contianed in
LinkageLocation for all of the Descriptor's parameters and return types are
sufficient. This CL therefore removes the MachineSignature from the
CallDescriptor and adjusts all the calling code accordingly, simplifying and
de-duplicating code in a bunch of places.

R=titzer@chromium.org, bmeurer@chromium.org
LOG=N

Review-Url: https://codereview.chromium.org/2124023003
Cr-Commit-Position: refs/heads/master@{#37633}