Backport r71704 (add configure check for C99 round function) to trunk.
diff --git a/Include/pymath.h b/Include/pymath.h
index 6ad174d..2cb2a23 100644
--- a/Include/pymath.h
+++ b/Include/pymath.h
@@ -22,6 +22,10 @@
 extern double copysign(double, double);
 #endif
 
+#ifndef HAVE_ROUND
+extern double round(double);
+#endif
+
 #ifndef HAVE_ACOSH
 extern double acosh(double);
 #endif