Amazingly, there were zero changes to the byte code generator and very
few changes to the interpreter - mainly because we've used good
abstractions that hide the differences between profiling and
non-profiling. So that bit was pleasantly straightforward, but there
were a pile of other wibbles to get the whole test suite through.
Note that a compiler built with -prof is now like one built with
-dynamic, in that to use TH you have to build the code the same way.
For dynamic, we automatically enable -dynamic-too when TH is required,
but we don't have anything equivalent for profiling, so you have to
explicitly use -prof when building code that uses TH with a profiled
compiler. For this reason Cabal won't work with TH. We don't expect
to ship a profiled compiler, so I think that's OK.