Fix a number of issues with the windows build

* Standardize on wprintf in pidgin/win32/winpidgin.c
* Use the inetc nsis plugin that supports https
* If building under msys2 copy libgcc_s_dw2-1.dll and libwinpthread to the
install directory.

Testing Done:
Ran successfully from the

* install directory
* online installer
* offline installer
* portable zip file

Reviewed at https://reviews.imfreedom.org/r/593/