PML: export bitcode pcmarker instructions
LegalizeDAG: PCMARKER should be removed during legalize unless supported by target
platin: refactoring

Splitting/merging Benedikt's patches in preparation for PC markers and user
flowfacts. This contains general refactoring, among it:
- filter pseudo .bc functions
- fixes for ruby-2.0/2.1
platin: preliminary support for markers