After adding the libtgvoip submodule its project was created by GYP
outside the project folder, because the relative path to libtgvoip.gyp
is "../ThirdParty/libtgvoip/" and projects are created in the same
relative folders.
Now we place MSVC and Xcode projects in tdesktop/Telegram, so the
libtgvoip project is created at tdesktop/ThirdParty/libtgvoip.