WebAssembly object file support in MC

Following up on recent patches which have added support for the new WebAssembly object file format in Object, I have a series of patches to add producer support in MC as well. Most of the code changes are in WebAssembly-specific files and directories, however two initial patches to add Triple support and create all the files needed for an MC backend reach into more target-independent areas of the tree, so ideally they should be reviewed by someone other than my WebAssembly colleagues :-).

If anyone is interesting in taking a look, they’re right here:

https://reviews.llvm.org/D26701 (just triple support)
https://reviews.llvm.org/D26722 (adds skeleton writer boilerplate)



Ping. I’m still looking for a reviewer for the MC skeleton patch. Thanks!