_configtest.c:1:5: warning: conflicting types for built-in function ‘exp’; expected ‘double(double)’ [-Wbuiltin-declaration-mismatch]
    1 | int exp (void);
      |     ^~~
_configtest.c:1:1: note: ‘exp’ is declared in header ‘<math.h>’
  +++ |+#include <math.h>
    1 | int exp (void);