Single-quoting ghc-options by space is wrong

If you put

```
ghc-options: -with-rtsopts="-A1000 -H1000 -K1000"
```

into your .cabal file, it will destroy your quoting by single-quoting with every space, calling ghc with

```
'ghc' ... '-with-rtsopts="-A1000' '-H1000' '-K1000"'
```

which will fail.

In `Distribution.Simple.GHC.buildExe`, it will have:

```
ghcOptExtra = ["-threaded","-with-rtsopts=\"-A1000","-H1000","-K1000\""],
```

Do you know why we actually single-quote everything in the first place?