do not redefine snprintf if it's already available

src/windows/port.cc

@@ -55,6 +55,7 @@ int safe_vsnprintf(char *str, size_t size, const char *format, va_list ap) {
   return _vsnprintf(str, size-1, format, ap);
 }
 
+#ifndef HAVE_SNPRINTF
 int snprintf(char *str, size_t size, const char *format, ...) {
   va_list ap;
   va_start(ap, format);
@@ -62,3 +63,4 @@ int snprintf(char *str, size_t size, const char *format, ...) {
   va_end(ap);
   return r;
 }
+#endif

src/windows/port.h

@@ -111,12 +111,16 @@ enum { STDIN_FILENO = 0, STDOUT_FILENO = 1, STDERR_FILENO = 2 };
  * because they don't always NUL-terminate. :-(  We also can't use the
  * name vsnprintf, since windows defines that (but not snprintf (!)).
  */
-extern int snprintf(char *str, size_t size,
+#ifndef HAVE_SNPRINTF
+extern int GOOGLE_GLOG_DLL_DECL snprintf(char *str, size_t size,
                                        const char *format, ...);
-extern int safe_vsnprintf(char *str, size_t size,
+#endif
+extern int GOOGLE_GLOG_DLL_DECL safe_vsnprintf(char *str, size_t size,
                           const char *format, va_list ap);
 #define vsnprintf(str, size, format, ap)  safe_vsnprintf(str, size, format, ap)
+#ifndef va_copy
 #define va_copy(dst, src)  (dst) = (src)
+#endif
 
 /* Windows doesn't support specifying the number of buckets as a
  * hash_map constructor arg, so we leave this blank.