CheckCXXSymbolExists: Make C++-syntax symbols work on more compilers

On some compilers the syntax `#ifndef std::fopen` will always lead to
compilation error.  Avoid generating it in the check.

1 files changed, 11 insertions, 0 deletions

diff --git a/Modules/CheckCXXSymbolExists.cmake b/Modules/CheckCXXSymbolExists.cmake
index b11209453d..5c9079dbf3 100644
--- a/Modules/CheckCXXSymbolExists.cmake
+++ b/Modules/CheckCXXSymbolExists.cmake
@@ -27,6 +27,17 @@ Check if a symbol exists as a function, variable, or macro in ``C++``.
   not be recognized: consider using the :module:`CheckTypeSize`
   or :module:`CheckCXXSourceCompiles` module instead.
 
+.. note::
+
+  This command is unreliable when ``<symbol>`` is (potentially) an overloaded
+  function. Since there is no reliable way to predict whether a given function
+  in the system environment may be defined as an overloaded function or may be
+  an overloaded function on other systems or will become so in the future, it
+  is generally advised to use the :module:`CheckCXXSourceCompiles` module for
+  checking any function symbol (unless somehow you surely know the checked
+  function is not overloaded on other systems or will not be so in the
+  future).
+
 The following variables may be set before calling this macro to modify
 the way the check is run: