USB_VBUS is not an alternate function, it is an additionnal function which is
always enabled.
If configured as an alternate function, it will draw current from VBUS.
All source files include general.h first and before anything else.
This inlcludes platform.h and platform_support.h
No header file needs to include to include any of these, but should include
any others needed for it's own declarations.
Uwe Bonnes
Nicolas Schodet
Gareth McMullin
Frantisek Burian