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, 13 insertions, 5 deletions

diff --git a/configure.in b/configure.in
index 1026c855bf2..e788419eb4f 100644
--- a/configure.in
+++ b/configure.in
@@ -2006,12 +2006,20 @@ case "$target" in
     ;;
 esac
 
-# isinf() could be a function or a macro (HPUX)
-AC_MSG_CHECKING(for isinf with <math.h>)
+# Check that isinf() is available in math.h and can be used in both C and C++ 
+# code
+AC_MSG_CHECKING(for isinf in <math.h>)
 AC_TRY_LINK([#include <math.h>], [float f = 0.0; int r = isinf(f); return r],
- AC_MSG_RESULT(yes)
- AC_DEFINE(HAVE_ISINF, [1], [isinf() macro or function]),
- AC_MSG_RESULT(no))
+  AC_MSG_RESULT(yes)
+  AC_MSG_CHECKING(whether isinf() can be used in C++ code)
+  AC_LANG_SAVE
+  AC_LANG_CPLUSPLUS
+  AC_TRY_LINK([#include <math.h>], [float f = 0.0; int r = isinf(f); return r],
+    AC_MSG_RESULT(yes)
+    AC_DEFINE(HAVE_ISINF, [1], [isinf() macro or function]),
+    AC_MSG_RESULT(no))
+  AC_LANG_RESTORE,
+  AC_MSG_RESULT(no))
  
 CFLAGS="$ORG_CFLAGS"