Duplicate landing pads generated

[smeenai]

https://godbolt.org/z/zrvbrqxEs has an example:

void f();
void g() {
    try {
        f();
        f();
    } catch (...) {}
}

CodeGen emits a single landing pad for the two calls, whereas with ClangIR you end up with duplicate landing pads (which aren't deduplicated even with LLVM optimizations). This ends up causing duplicating in the EH tables as well: https://godbolt.org/z/9aTnWjxEq. It shouldn't cause any correctness issues but it'll increase code size a bit until we address it.

[bcardosolopes]

I have plans for this but didn't file an issue yet, thanks for getting to it first. Assigning to me for now.