Fix for bug #28240: "isinf()" cannot be used in C++ for lack of prototype

- Since isinf() portability across various platforms and
  compilers is a complicated question, we should not use
  it directly. Instead, the my_isinf() macro should be used,
  which is defined as an alias to the system-defined isinf()
  if it is safe to use, or a workaround implementation otherwise


configure.in:
  Added a check to define HAVE_ISINF only if it can be used
  in C++ code as well.
include/my_global.h:
  Define my_isinf() as an alias to isinf(), if it is available
  in both C and C++ code. Otherwise, define it to a workaround
  implementation.
sql/item_func.cc:
  Replaced isinf() with my_isinf().
strings/strtod.c:
  Replaced isinf() with my_isinf().

1 files changed, 5 insertions, 6 deletions

diff --git a/include/my_global.h b/include/my_global.h
index e9b371d8d30..f32a987ffb1 100644
--- a/include/my_global.h
+++ b/include/my_global.h
@@ -792,12 +792,11 @@ typedef SOCKET_SIZE_TYPE size_socket;
 #define isnan(x) ((x) != (x))
 #endif
 
-#if !defined(HAVE_ISINF)
-/* The configure check for "isinf with math.h" has failed */
-#ifdef isinf
-#undef isinf
-#endif
-#define isinf(X) (!finite(X) && !isnan(X))
+#ifdef HAVE_ISINF
+/* isinf() can be used in both C and C++ code */
+#define my_isinf(X) isinf(X)
+#else
+#define my_isinf(X) (!finite(X) && !isnan(X))
 #endif
 
 /* Define missing math constants. */