Based on @noahpistilli (Sketch) PR:
https://github.com/dolphin-emu/dolphin/pull/12567
Fixed the Windows support and the heisenbug caused by uninitialized
members.
Config system integration finalized.
This reverts commit fb265b610d.
The optimization in that commit is safe when the executor thread is
writing and the GUI thread is reading, but I had failed to take into
account that it's unsafe when the GUI thread is writing and the executor
thread is reading. (The native UpdateAdditionalMetadata function loops
through m_cached_files, which is unsafe if another thread is adding
elements to m_cached_files simultaneously.)
Losing out on this optimization isn't too bad, because
719930bb39 makes it very unlikely that
both threads will want the lock at the same time.
* moves dolphin-specific settings out of Base.props
* creates exports.props for externals, allowing to easily import
individual Externals
* corrects some cruft that accumulated and probably contributed
to msbuild overbuilding
