Struct parsing produces incorrect size for structs containing conditional defines

[jkehne]

When parsing a C struct containing conditional #defines in its definition, idl4 will calculate the struct's size to be 4 bytes larger than it actually is. If such a struct is used as a parameter in an interface, this will result in all parameters following that struct to be skewed by one MR (the stub code will copy the correct payload, but set the number of untyped words in the message one too high).
This affects all L4 system structs containing the __PLUS32-macro from l4/types.h (e.g. L4_ThreadId_t).