Documentation Issue using MinGW

We use the MinGW toolchain that ships with the Qt Libraries. This is the output of gcc -v

```
Thread model: posix
gcc version 5.3.0 (i686-posix-dwarf-rev0, Built by MinGW-W64 project)
```

Using **BOOST_STACKTRACE_USE_WINDBG** with MinGW results in linker errors because the following libraries are required: **ole32** and **dbgeng**. This is not documented anywhere.