I made sure to create a merge conflict with the code attached to ticket #229
(which comments this code out due to changes in the DMD 'Type' type hierarchy)
so that if it gets committed as-is there will be a human looking at it.
- See through typedefs and enums in passByVal
- Don't depend on TypeFunction::parameters->dim being the actual number of
parameters; it contains unexpanded tuples as single elements.
- Implement x86-64 extern(C), hopefully correctly.
- Tried to be a bit smarter about extern(D) while I was there.
Interestingly, this code seems to be generating more efficient code than
gcc and llvm-gcc in some edge cases, like returning a `{ [7 x i8] }` loaded from
a stack slot from an extern(C) function. (gcc generates 7 1-byte loads, while
this code generates a 4-byte, a 2-byte and a 1-byte load)
I also added some changes to make sure structs being returned from functions or
passed in as parameters are stored in memory where the rest of the backend seems
to expect them to be. These should be removed when support for first-class
aggregates improves.