Adding verbiage to the Language Extensions document about __has_include and __has_inc...

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172643 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/docs/LanguageExtensions.rst b/docs/LanguageExtensions.rst
index be54402fd3f035818ab091685d63f8bf7433fe51..2abbea7da6941a200d353ce8ae646756d32ce0a3 100644 (file)
--- a/docs/LanguageExtensions.rst
+++ b/docs/LanguageExtensions.rst
@@ -140,7 +140,8 @@ Include File Checking Macros
 Not all developments systems have the same include files.  The
 :ref:`langext-__has_include` and :ref:`langext-__has_include_next` macros allow
 you to check for the existence of an include file before doing a possibly
-failing ``#include`` directive.
+failing ``#include`` directive.  Include file checking macros must be used 
+as expressions in #if or #elif preprocessing directives.
 
 .. _langext-__has_include: