runtime.Func.{Name,FileLine} need to be able to
go from a *_func to a funcInfo. The missing bit of
information is what module contains that *_func.
The existing implementation looked up the module
using the *_func's entry PC. A subsequent change will
store *_func's entry PC relative to the containing module.
Change the module lookup to instead for the module
whose pclntable contains the *_func,
cutting all dependencies on the contents of the *_func.