I just tried building and installing binutils from sid on jessie, and then building a kernel module for the current kernel on the machine. Module built with binutils from jessie loads fine, modules built with binutils from sid has the mcount symbol error.
So I would agree, these two bugs do not appear to be the same even though they seem to have appeared at the same time (both are triggered by changes in binutils, but not the same change most likely). The ppc64le does look like the missing weak symbols are the problem, and powerpc64 seems to be something else (since the powerpc64 kernel never had the symbol that ppc64le says it can't find). -- Len Sorensen