Clang doesn't have function multi-versioning (FMV), but it now supports the ifunc attribute for runtime resolution:

http://clang.llvm.org/docs/AttributeReference.html#ifunc-gnu...

Google says no.

Here is a pdf reviewing work on this[0], I guess. It is two years old though:

[0] http://llvm.org/devmtg/2014-10/Slides/Christopher-Function%2...

Not sure about those, but Intel compiler (C and Fortran) has had it for a long time.