Vala `size_t` does not match C `size_t` on Mingw64

Vala size_t is mapped to gsize. On MSYS, this maps to long long int (8 bytes).

But on MSYS, size_t is long int, which is also 8 bytes, but GCC doesn't like it and complains that the type is incompatible.

Use case: I am trying to implement a C API in Vala, so the Vala-generated C is compiled with a handwritten C header file.

My workaround was to copy the definitions for size_t and ssize_t from posix.vapi into my project (since by they are only available from 'posix.vapi' in the 'posix' profile).

I guess that the current definitions may be entrenched enough that they can't be changed, but it would be good to document this problem somewhere.