Add mingw32-libpcre as dependency

This enables us to compile git against libpcre.
And this makes thing like
```
git grep -P "\bpcre\b" HEAD
```
possible.
Which I already did in https://github.com/t-b/git/tree/use-libpcre. And all tests still pass with that too.
Exactly, runtime dependencies need to go to the package xml file, not to the installer.