GHC Stack on `error` with ghc 8.2

TheFile.lhs

I was told compiling with `prof` will make the new GHC call stacks more informative (which seems odd) so I made this test.

Consider `so.hs`:

> import GHC.Stack
>
> main :: IO ()
> main = f
>
> f, g, h :: IO ()
> f = g
> g = h
> h = error "oh nos!"

```
tommd@HalfAndHalf /tmp% ghc -O0 -fforce-recomp so.hs && ./so
[1 of 1] Compiling Main             ( so.hs, so.o )
Linking so ...
so: oh nos!
CallStack (from HasCallStack):
  error, called at so.hs:9:5 in main:Main
tommd@HalfAndHalf /tmp% ghc -O0 -fforce-recomp -prof so.hs && ./so
[1 of 1] Compiling Main             ( so.hs, so.o )
Linking so ...
so: oh nos!
CallStack (from HasCallStack):
  error, called at so.hs:9:5 in main:Main
CallStack (from -prof):
  Main.CAF (<entire-module>)
```
  
So that wasn't too interesting, but if we do the normal thing and use `HasCallStack => IO ()` as the types then we'd get:

```
tommd@HalfAndHalf /tmp% ghc -O0 -fforce-recomp so.hs && ./so
[1 of 1] Compiling Main             ( so.hs, so.o )
Linking so ...
so: oh nos!
CallStack (from HasCallStack):
  error, called at so.hs:9:5 in main:Main
  h, called at so.hs:8:5 in main:Main
  g, called at so.hs:7:5 in main:Main
  f, called at so.hs:4:8 in main:Main
  main, called at so.hs:4:1 in main:Main
```

Which is what you've probably seen elsewhere on the web wrt GHC call stacks.