[cecilia] Make stddef.h types primitive IDL types
When making a program containing wrappers for several stdio functions, I saw that the toolchain doesn't currently have special handling for the likes of 'size_t'.
Attached is a patch that makes size_t, ptrdiff_t and wchar_t (all three from stddef.h, used in various other standard headers) primitive types in idl-parser, and checks that they work as such in cecilia-adl. Please review :)
IMO, this should be backported to the Cecilia 2.0.x series, so that it can be used in what Germain (mostly) and I (intermittently) are working on.