Fix link step on MinGW

Fix link step on MinGW

.def files are handled differently on MinGW than MSVC for the WIN32 target:

```
[ 14%] Linking C shared library libexpat.dll
/usr/lib/gcc/x86_64-w64-mingw32/9.1.0/../../../../x86_64-w64-mingw32/bin/ld: ../lib/libexpat.def:4: syntax error
/usr/lib/gcc/x86_64-w64-mingw32/9.1.0/../../../../x86_64-w64-mingw32/bin/ld:../lib/libexpat.def: file format not recognized; treating as linker script
/usr/lib/gcc/x86_64-w64-mingw32/9.1.0/../../../../x86_64-w64-mingw32/bin/ld:../lib/libexpat.def:1: syntax error
collect2: error: ld returned 1 exit status
```