Sema: emits incorrect safety check for integer vector division

[jacobly0]

var lhs: @Vector(2, i8) = .{ -128, 0 };
const rhs: @Vector(2, i8) = .{ 1, -1 };
pub fn main() void {
    _ = @divTrunc(lhs, rhs);
}

$ zig run repro.zig
thread 476777 panic: integer overflow
repro.zig:4:9: 0x103a524 in main (repro)
    _ = @divTrunc(lhs, rhs);
        ^
lib/std/start.zig:647:22: 0x1039f72 in posixCallMainAndExit (repro)
            root.main();
                     ^
lib/std/start.zig:271:5: 0x1039b4d in _start (repro)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
Aborted (core dumped)

As an added bonus for fixing this bug, you can delete the lines in test/behavior/x86_64/math.zig referencing this issue!