headers: Include codecapi.h in uuids.h and define UUID_GEN if INITGUID is defined

Without this, the guids defined in codecapi.h essentially can't be
used.

Signed-off-by: Martin Storsjö <martin@martin.st>

mingw-w64-headers/include/uuids.h

diff --git a/mingw-w64-headers/include/uuids.h b/mingw-w64-headers/include/uuids.h
index ec93ec2..1af246a 100644
--- a/mingw-w64-headers/include/uuids.h
+++ b/mingw-w64-headers/include/uuids.h
@@ -363,6 +363,11 @@
 OUR_GUID_ENTRY(CODECAPI_ALLSETTINGS,0x6a577e92,0x83e1,0x4113,0xad,0xc2,0x4f,0xce,0xc3,0x2f,0x83,0xa1)
 OUR_GUID_ENTRY(CODECAPI_SUPPORTSEVENTS,0x0581af97,0x7693,0x4dbd,0x9d,0xca,0x3f,0x9e,0xbd,0x65,0x85,0xa1)
 OUR_GUID_ENTRY(CODECAPI_CURRENTCHANGELIST,0x1cb14e83,0x7d72,0x4657,0x83,0xfd,0x47,0xa2,0xc5,0xb9,0xd1,0x3d)
+
+#ifdef INITGUID
+#define UUID_GEN
+#include <codecapi.h>
+#endif
 #endif
 
 #undef OUR_GUID_ENTRY