Fix up the PEi386 linker well enough for ghci to start and function
on Win32.  Two potential problems still to be fixed properly:

* ocGetNames_PEi386 doesn't copy local syms into oc's local symtab,
  and it probably should (since the ELF one does).  Easy to fix.

* I can't figure out how to read syms in the executable itself
  on Win32.  This problem is solved properly for Unix-ELF by doing
  dlopen(NULL).  Here I have kludged it using RTS_MINGW_ONLY_SYMBOLS,
  but this is not a good long-term solution.