SOUNDWAVE_USING_WINMM section should include mmeapi.h

[MaGetzUb]

When you use the default WINMM backend, some winapi macros may disable including mmeapi.h from the Windows.h, therefore HWAVEOUT handles and other WINMM things become undefined. My suggestion is to add #include <mmeapi.h> after #include <windows.h> in the WINMM backend.