stage1 C ABI compatibility

[andrewrk]

This issue is to track C ABI compatibility support in the stage1 compiler.

Here's what support looks like currently:

• integers, floats, pointers, enums, bools work on every target, as parameters and return values
• x86_64: struct & union parameters & return values larger than 16 bytes
• x86_64: struct & union parameters that have at least 1 integer in them
• x86_64: struct & union parameters <= 16 bytes which break structs into parameters
• x86_64: struct & union parameters <= 16 bytes which are all floats
• x86_64: struct & union return values <= 16 bytes
• ARM: struct & union return values
• ARM: struct & union parameters
• C ABI for parameters that is unsupported gives a compile error linking to this issue
• C ABI for return values that is unsupported gives a compile error linking to this issue
• other architectures structs & unions parameters & return values

For those who find this issue from the compile error, leave a comment detailing your specific needs and I'll see if I can code those up for you to unblock you, so you don't have to wait for this issue to be 100% solved.

[andrewrk]

Update:

I just merged a branch into master which does the following things:

• Unsupported C ABI gives a compile error, like this:

const ASmallUnion = extern union {
    r: u8,
};
extern fn foo(x: ASmallUnion) void;

pub fn main() void {
    const x = ASmallUnion{ .r = 0x12 };

    foo(col);
}

/home/andy/downloads/zig/build/test.zig:4:8: error: TODO: support C ABI for more targets. https://github.com/ziglang/zig/issues/1481
extern fn foo(x: ASmallUnion) void;
       ^
/home/andy/downloads/zig/build/test.zig:4:8: note: pointers, integers, floats, bools, and enums work on all targets
extern fn foo(x: ASmallUnion) void;
       ^

• There is a new type of test, C ABI tests, which covers the C ABI that we do suport. See test/stage1/c_abi/* for the source.

Test 1/9 C importing Zig ABI Tests...OK
Test 2/9 C ABI integers...OK
Test 3/9 C ABI floats...OK
Test 4/9 C ABI pointer...OK
Test 5/9 C ABI bool...OK
Test 6/9 C ABI array...OK
Test 7/9 C ABI big struct...OK
Test 8/9 C ABI big union...OK
Test 9/9 C ABI small struct of ints...OK

• Added all targets C ABI support for integers, floats, bools, enums, and pointers
• Added x86_64 C ABI support for big structs and unions (which are passed by memory)
• Added x86_64 C ABI support for small structs which contain at least one integer

[andrewrk]

Zig will now either panic or emit a compile error when C ABI compatibility is required that it doesn't support yet. Therefore this issue is now an enhancement in order to provide additional C ABI compatibility and not a bug.

For those who find this issue from the compile error, leave a comment detailing your specific needs and I'll see if I can code those up for you to unblock you, so you don't have to wait for this issue to be 100% solved.