In order to reduce our reliance on __builtin_{ffs, clz, ctz, popcount},
this commit removes all calls to these functions and replaces them with
the equivalent functions in AK/BuiltinWrappers.h.
This should make debugging and profiling much better, at little to no
runtime cost.
Also moves off the operator definitions to a separate header, so it
should also improve the editing experience quite a bit.
