Custom `sinc` path not working

Hi @wsmoses,

Thank you for the guidance today!

## Pre-Defined sinc paths

I was trying if a self-defined function called `sinc` is picked up and replaced with the [pre-defined custom paths](https://github.com/EnzymeAD/Enzyme/blob/v0.0.197/enzyme/Enzyme/InstructionDerivatives.td#L489-L497), and it does not seem to work as expected:
https://fwd.gymni.ch/DdjNuM
```C++
#include
#include

double sinc (double x) {
return std::sin(x) / x;
}

double __enzyme_autodiff(void*, double);
int main() {
double x = 3.14;

double grad_x = __enzyme_autodiff((void*)sinc, x);
printf("sinc'(%f) = %f\n", x, grad_x); // -0.318632

x = 0;
double grad_x00 = __enzyme_autodiff((void*)sinc, x);
printf("sinc'(%f) = %f\n", x, grad_x00); // 0.0

return 0;
}
```
```
sinc'(3.140000) = -0.318632
sinc'(0.000000) = -5486124068873210445588960243682892870359454172549082081269977249875439498450530608481829736532482212550881929053150599861406478595121674729324160965665746675952409952613381490567235017715679668230311379032918639874384375900517443469363980679948746539362679355976183938475470978590331407354983321197084672.000000
```

## Enzyme Function-Like "sinc"

I then tried `enzyme_function_like` but that does not do the trick either:
https://fwd.gymni.ch/DHb8VC
```C++
#include
#include

__attribute__((enzyme_function_like("sinc")))
double my_sinc (double x) {
return std::sin(x) / x;
}

double __enzyme_autodiff(void*, double);
int main() {
double x = 3.14;

double grad_x = __enzyme_autodiff((void*)my_sinc, x);
printf("sinc'(%f) = %f\n", x, grad_x); // -0.318632

x = 0;
double grad_x0 = __enzyme_autodiff((void*)my_sinc, x);
printf("my_sinc'(%f) = %f\n", x, grad_x0); // 0.0

return 0;
}
```
```
sinc'(3.140000) = -0.318632
my_sinc'(0.000000) = -nan
```

What am I missing? :)