https://github.com/esp8266/Arduino/pull/8116

whythough.c

#include <stdio.h>
#include <math.h>
#include <stdlib.h>

double handle_doubles(double input) {
        return fabs(input);
}

float handle_floats(float input) {
        return fabsf(input);
}

long handle_long(long input) {
        return labs(input);
}

#define abs(x)\
    __builtin_choose_expr(\
        __builtin_types_compatible_p(typeof(x), double),\
        handle_doubles(x),\
        __builtin_choose_expr(\
            __builtin_types_compatible_p(typeof(x), float),\
            handle_floats(x),\
                handle_long((long)x)))

int main() {
        float a = 0.f;
        double b = -5.;
        int c = 0;

        printf("%f\n", abs(a));
        printf("%f\n", abs(b));
        printf("%ld\n", abs(c));

}