Hook up SDL_acos and SDL_asin properly.

src/stdlib/SDL_stdlib.c

@@ -46,6 +46,42 @@ SDL_atan2(double x, double y)
 #endif /* HAVE_ATAN2 */
 }
 
+double
+SDL_acos(double val)
+{
+#if defined(HAVE_ACOS)
+    return acos(val);
+#else
+    double result;
+    if (val == -1.0) {
+        result = M_PI;
+    } else {
+        result = SDL_atan(SDL_sqrt(1.0 - val * val) / val);
+        if (result < 0.0)
+        {
+            result += M_PI;
+        }
+    }
+    return result;
+#endif
+}
+
+double
+SDL_asin(double val)
+{
+#if defined(HAVE_ASIN)
+    return asin(val);
+#else
+    double result;
+    if (val == -1.0) {
+        result = -(M_PI / 2.0);
+    } else {
+        result = (M_PI / 2.0) - SDL_acos(val);
+    }
+    return result;
+#endif
+}
+
 double
 SDL_ceil(double x)
 {