Add optional warnings to bad libm functions

libc/math/bad.c

@@ -1,22 +1,31 @@
 /* STUB MATH LIBRARY */
+#include <stdio.h>
+#include <stdlib.h>
+
+#define BAD do { if (getenv("LIBM_DEBUG")) { fprintf(stderr, "Called bad math function %s\n", __func__); } } while (0)
 
 double acos(double x) {
+	BAD;
 	return 0.0;
 }
 
 double asin(double x) {
+	BAD;
 	return 0.0;
 }
 
 double atan(double x) {
+	BAD;
 	return 0.0;
 }
 
 double ceil(double x) {
+	BAD;
 	return 0.0; /* extract and convert? */
 }
 
 double cosh(double x) {
+	BAD;
 	return 0.0;
 }
 
@@ -30,26 +39,32 @@ double ldexp(double a, int exp) {
 }
 
 double log(double x) {
+	BAD;
 	return 0.0;
 }
 
 double log10(double x) {
+	BAD;
 	return 0.0;
 }
 
 double log2(double x) {
+	BAD;
 	return 0.0;
 }
 
 double sinh(double x) {
+	BAD;
 	return 0.0;
 }
 
 double tan(double x) {
+	BAD;
 	return 0.0;
 }
 
 double tanh(double x) {
+	BAD;
 	return 0.0;
 }