[msbuild] When doing device-specific builds, ignore incompatible device OS's
If the user has tvOS, watchOS, and iOS projects in their solution
and goes to build for one of them for a specific device, it passes
along the device specific info to MSBuild. The build would then
fail for the tvOS and/or watchOS projects because of incompatible
architecture requirements.
This fixes that problem by short-cutting the ParseDeviceSpecificBuildInfo
task to output the default values (the values used when not building
for a specific device).
Jeffrey Stedfast
Rolf Bjarne Kvinge