Properly handle indirect arguments for external C functions

[ggiraldez]

Fixes #9533

• When making a call to a C function with an indirect argument, make a caller allocated copy and substitute the argument with a pointer to the copy
• Do not attempt to cast an indirect argument on the receiving side
• Enable pending spec in AArch64 and Windows 64 (from C ABI: Add a spec for accepting a large struct - failing on win32, aarch64 #9534)

From the description of #9533 and linked issues I gather the C ABI argument passing was ported from Rust, which has the concept of indirect argument passing. Reading the ABI specs for ARM64 (see section 5.4.2, B-3) and for Windows 64 x86, and analyzing the LLVM IR code generated by Clang, it's clear that an indirect argument should be passed as a pointer to caller-allocated memory. This is different than passing an argument on the stack, which seems to be the default in Linux and Darwin on x86: this is handled by LLVM when the argument is annotated with byval, and the generated assembly code pushes the value on the stack instead of passing it on a register.

This PR fixes two problems, one on the caller and one on the callee:

• On the caller, when an argument should be passed indirectly, it allocates stack memory to hold a copy and the pointer to the allocated memory is passed instead.
• On the callee, when receiving an indirect argument, no special cast/copy is attempted as the code can modify the memory on the passed pointer freely.

The change in fun.cr is pretty ugly, but I don't currently know what are all the cases it should cover and it's not immediately obvious from the code. The method create_local_copy_of_arg is doing way too much already IMHO.

[asterite]

This is great, thank you! ❤️

[oprypin]

Ooooh yes it works

Peek.2021-09-09.23-04.mp4