This is a revisit to D20749 which introduces a flag that enables the relative ABI described in https://bugs.llvm.org/show_bug.cgi?id=26723.
This is still a work in progress and am still in the process of debugging some issues I ran into when building Fuchsia with this, but wanted to raise some awareness and see if anyone has any thoughts or comments.
Should we proactively generalize this as a "CXXABIVariant" enum, which for now can just be "Standard" and "RelativeVTables"?
Also, I don't want to pre-empt your secret plans, but if Fuchsia is just going to use this as its system C++ ABI, maybe we should plan for that, too.