suspensions inside for loops generate invalid LLVM IR

[andrewrk]

const std = @import("std");
const expect = std.testing.expect;

var global_frame: ?anyframe = null;

test "suspend in for loop" {
    _ = async atest();
    while (global_frame) |f| resume f;
}

fn atest() void {
    expect(func([_]u8{ 1, 2, 3 }) == 6);
}
fn func(stuff: []const u8) u32 {
    global_frame = @frame();
    var sum: u32 = 0;
    for (stuff) |x| {
        suspend;
        sum += x;
    }
    global_frame = null;
    return sum;
}

Expected to pass. Instead:

Instruction does not dominate all uses!
  %8 = load i64, i64* %7, align 8, !dbg !1349
  %10 = icmp ult i64 %9, %8, !dbg !1349
Instruction does not dominate all uses!
  %13 = getelementptr inbounds i8, i8* %12, i64 %9, !dbg !1349
  %17 = load i8, i8* %13, align 1, !dbg !1356
Instruction does not dominate all uses!
  %9 = load i64, i64* %i, align 8, !dbg !1349
  %22 = add nuw i64 %9, 1, !dbg !1349
LLVM ERROR: Broken module found, compilation aborted!

The implementation needs to spill some more values here to make this work.