This patch adds support for multiple return values from ccall in cmm to be used with C functions, that return structure by value. In that case ccall should be annotated with structure layout information, see test cases for example.
It should work for linux/x86, linux/x86_64, windows x86, windows/x64, mac os X x86_64
Not implemented for llvm backend yet.
Not sure what to do with PPC and SPARC backends