COFF support for Win32

These are the changes for COFF support for Win32. It uses CRuntime_DigitalMars/CRuntime_Microsoft instead of Win32/Win64 where appropriate. Most of the exisiting adhoc version identifiers are not yet replaced.

compile from the VS command line with

```
make -f win64.mak MODEL=32mscoff "CC=\"%VCINSTALLDIR%\bin\cl.exe\"" "AR=\"%VCINSTALLDIR%\bin\lib.exe\""
```

For building and running unittests, an appropriate curl.lib needs to be generated.