Add prototypes to get the mathmodule.c to compile on OSF1 5.1 (Tru64)

and eliminate a compiler warning in floatobject.c.  There might be
a better way to go about this, but it should be good enough for now.

Modules/mathmodule.c

@@ -12,6 +12,11 @@ extern double modf (double, double *);
 #endif /* __STDC__ */
 #endif /* _MSC_VER */
 
+#ifdef _OSF_SOURCE
+/* OSF1 5.1 doesn't make this available with XOPEN_SOURCE_EXTENDED defined */
+extern double copysign(double, double);
+#endif
+
 /* Call is_error when errno != 0, and where x is the result libm
  * returned.  is_error will usually set up an exception and return
  * true (1), but may return false (0) without setting up an exception.

Objects/floatobject.c

@@ -16,6 +16,11 @@ extern double fmod(double, double);
 extern double pow(double, double);
 #endif
 
+#ifdef _OSF_SOURCE
+/* OSF1 5.1 doesn't make this available with XOPEN_SOURCE_EXTENDED defined */
+extern int finite(double);
+#endif
+
 /* Special free list -- see comments for same code in intobject.c. */
 #define BLOCK_SIZE	1000	/* 1K less typical malloc overhead */
 #define BHEAD_SIZE	8	/* Enough for a 64-bit pointer */