builder: runtime.buildVersion not a string

[ydnar]

When running tests under -target=wasip2, the build for #4809 was failing when testing crypto/elliiptic:

$ tinygo test -v -target=wasip2 crypto/elliptic
FAIL	crypto/elliptic	0.000s
runtime.buildVersion: not a string

I traced the issue to an error type in package internal/cm:

var (
	errEmpty          = &stringError{err: "empty text"}
	errNoMatchingCase = &stringError{err: "no matching case"}
)

type stringError struct {
	_   struct{}
	err string
}

func (err *stringError) Error() string {
	return err.err
}

Removing this type fixes the build-time error.

[aykevl]

That's definitely not supposed to happen!
How can I reproduce this?

[aykevl]

Oh I have a reproducer.
At commit afd4dc2, I got:

$ tinygo run -target=wasip2 ./testdata/alias.go
runtime.buildVersion: not a string

[aykevl]

Huh. It looks like LLVM has decided that { ptr, i32 } and %runtime._string are the same type. And they do have the same layout in memory. But this is a bit unexpected.

[aykevl]

This fixes the bug: #4811