Upstream commit dddccbc3ef50ac52bf00723fd2f68d98140aab80
* adds ucrtbase.def.in
* mingwex: replace mingw crt files with ucrt files
* adds missing mingw-w64 ucrt files
The rules that govern which set of files are included or excluded is
contained in the logic for tools/update_mingw.zig
I've added more of the ".def" files from mingw. The list is based on all the libraries referenced by the win32metadata project. (see https://github.com/marlersoft/zigwin32).