gio: Add private headers with missing UWP/COM types

MinGW-w64 lacks the appropriate headers, so we have to add them
here. Note that these only have the C versions (normally these
things come in both C and C++ flavours), since that's what we use.

Also note that some of the functions that we don't use (but must
describe to maintain binary compatibility) were altered to use
IUnknown (basically, an untyped pointer) instead of the appropriate
object types, as adding these types would require other types,
which would pull even more types, forcing us to drag half of the
UWP headers in here. By replacing unused types with IUnknown we
can trim a lot of branches from the dependency graph.

gio/gwin32api-misc.h

@@ -0,0 +1 @@
+typedef interface IProcessorArchitecture IProcessorArchitecture;