Update depends on qt to build the whole qtbase and preserve cmake/mkspecs

Summary: This ensure that we can use Qt's cmake integration when using Qt from depends.

Test Plan:

cd build
make -C ../depends HOST=i686-w64-mingw32

Checks that cmake files and mkdepends are installed properly.

Reviewers: schancel, #bitcoin_abc

Reviewed By: schancel, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D830