Avoid issue with ISO C90 compilers ("this decimal constant is unsigned only in ISO C90")
Implement real-time-milliseconds for all targets of _t-univ.scm
Introduce ___SIZE_T, ___SSIZE_T and ___PTRDIFF_T to handle memory models where "long int" is not the same size as "void*" (e.g. on 64bit Windows which uses a IL32LLP64 memory model)