This reverts commit 135b91aecd9be1f6f5806b667e07e383dd481198.
"endsWithBreak()" is not a meaningful question to ask and should not be
used this way. A simple example that defeats this logic is:
```zig
export fn entry() void {
outer: {
{
break :outer;
}
return;
}
}
```
Block statements that end with "break" should not be considered
"noreturn" for the enclosing scope, but other "noreturn" instructions
(return, panic, compile error, etc.) should be. This differentiation
necessitates handling "break" differently from the other "noreturn"
instructions when inside a block statement.
As demonstrated by this new test case, stage1's functionality is
incorrect since it does not handle slicing from len..len correctly.
stage2 already has the correct behavior here.
Prior to this change, for an example compiler error test case with
multiple identical errors messages such as
```
:1:2: error: foo
:1:2: error: foo
```
the test harness would never increment the error index thus only
marking the very first error message as handled yielding a false
positive.
Additionally, while here, regress `dereference_anyopaque` test case
as not passing on `wasm32-wasi` target.
Additionally:
* Sema: fix array cat/mul not setting the sentinel value
- This required an LLVM backend enhancement to the handling of the
AIR instruction aggregate_init that likely needs to be
propagated to the other backends.
* Sema: report integer overflow of array concatenation in a proper
compile error instead of crashing.
* Sema: fix not using proper pointer address space for array cat/mul
* `?E` where E is an error set with only one field now lowers the same
as `bool`.
* Fix implementation of errUnionErrOffset and errUnionPayloadOffset to
properly compute the offset of each field. Also name them the same
as the corresponding LLVM functions and have the same function
signature, to avoid confusion. This fixes a bug where wasm was
passing the error union type instead of the payload type.
* Fix C backend handling of optionals with zero-bit payload types.
* C backend: separate out airOptionalPayload and airOptionalPayloadPtr
which reduces branching and cleans up control flow.
* Make Type.isNoReturn return true for error sets with no fields.
* Make `?error{}` have only one possible value (null).
