Proposal: Move architecture-specific information from std.builtin to @import("builtin")

[Snektron]

Currently, std.builtin contains architecture-specific information about calling conventions:

zig/lib/std/builtin.zig

Lines 156 to 172 in 9de452f

	pub const CallingConvention = enum {
	Unspecified,
	C,
	Naked,
	Async,
	Inline,
	Interrupt,
	Signal,
	Stdcall,
	Fastcall,
	Vectorcall,
	Thiscall,
	APCS,
	AAPCS,
	AAPCSVFP,
	SysV,
	};

Using architecture-specific calling conventions on the improper architecture yields a compile-error as expected.

With relevance to #653, I believe this information should be moved to std.target, so that address space definitions (which are also architecture-specific) can also live there. Note that calling conventions share a good portion of calling conventions, so maybe this requires some .ArchitectureSpecific: std.target.CallingConvention variant in std.builtin.CallingConvention.

On a side note, maybe std.builtin and @import("builtin") should not have the same name.

[marler8997]

My guess is that stuff goes into the builtin module if the compiler "depends" on it. I think the compiler avoids depending on anything in std other than what's in the builtin module.

[nektro]

i think std.builtin is for the stuff that doesn't change (ie the types of things). builtin.zig is generated by the compiler and saved in zig-cache