Extern codegen generates multiple function with the same name and different types

[yamaguchi1024]

@proc
def foo_sigmoid(xo : f32, yo : f64, xi : f32, yi : f64):
    xo = sigmoid(xi)
    yo = sigmoid(yi)

generates a C file that starts with

#include <math.h>
double sigmoid(double x) {
    return 1 / (1 + exp(-x));
}

#include <math.h>
float sigmoid(float x) {
    return 1 / (1 + exp(-x));
}

which is invalid (C does not support function overloading).