Segfault at runtime when calling a function from an `@export`'d function pointer

[Jarred-Sumner]

Zig Version

0.13.0

Steps to Reproduce and Observed Behavior

To reproduce:

1. Run zig test on this file:

   
   fn function() callconv(.C) void {}
   const exported = &function;
   comptime {
   @export(exported, .{ .name = "exported2" });
   }

extern fn exported2() void;

test { exported2(); }

2. Output:
```zig
Bus error at address 0x1029a4150
Panicked during a panic. Aborting.
error: the following test command crashed:
/Users/jarred/Code/bun/.zig-cache/o/3c26355fcac2b8e03bcdb703800c6976/test

This reproduces on macOS arm64 and Windows x64. It caused the "fuzzy-wuzzy.test.ts" test to fail in this github action run (and locally in a build with optimizations enabled).

• The calling convention specified doesn't seem to matter, it happens for both .SysV and .C on Windows x64.
• The "name" doesn't seem to matter, it happens when the name is the same as the function name

Expected Behavior

The test should pass without crashing

[llogick]

The technical aspect of this is that the code is exporting the equivalent of *const *const fn () callconv(.C) void while the extern fn exported2() void; is expecting a *const fn () callconv(.C) void.

To handle that

const exported2 = @extern(*const *const fn () callconv(.C) void, .{ .name = "exported2" });
...
    exported2.*();
...

[Vexu]

This footgun should be addressed by this accepted proposal #14911