doc/cpp: Document __has_include_next

While hacking on an unrelated change, I noticed that __has_include_next
hasn't been documented at all.  This patch adds it to the __has_include
manual node.

gcc/ChangeLog:

	* doc/cpp.texi (__has_include): Document __has_include_next
	also.
	(Conditional Syntax): Mention __has_include_next in the
	description for the __has_include menu entry.

1 files changed, 24 insertions, 16 deletions

diff --git a/gcc/doc/cpp.texi b/gcc/doc/cpp.texi
index a83aa26..970c0a3 100644
--- a/gcc/doc/cpp.texi
+++ b/gcc/doc/cpp.texi
@@ -3204,7 +3204,8 @@ directive}: @samp{#if}, @samp{#ifdef} or @samp{#ifndef}.
 * @code{__has_builtin}::
 * @code{__has_feature}::
 * @code{__has_extension}::
-* @code{__has_include}::
+* @code{__has_include}::        @code{__has_include} and
+                                 @code{__has_include_next}
 * @code{__has_embed}::
 @end menu
 
@@ -3607,22 +3608,27 @@ details of which identifiers are accepted by these function-like macros, see
 the Clang documentation}}.
 
 @node @code{__has_include}
-@subsection @code{__has_include}
+@subsection @code{__has_include}, @code{__has_include_next}
 @cindex @code{__has_include}
-
-The special operator @code{__has_include (@var{operand})} may be used in
-@samp{#if} and @samp{#elif} expressions to test whether the header referenced
-by its @var{operand} can be included using the @samp{#include} directive.  Using
-the operator in other contexts is not valid.  The @var{operand} takes
-the same form as the file in the @samp{#include} directive (@pxref{Include
-Syntax}) and evaluates to a nonzero value if the header can be included and
-to zero otherwise.  Note that that the ability to include a header doesn't
-imply that the header doesn't contain invalid constructs or @samp{#error}
-directives that would cause the preprocessor to fail.
-
-The @code{__has_include} operator by itself, without any @var{operand} or
-parentheses, acts as a predefined macro so that support for it can be tested
-in portable code.  Thus, the recommended use of the operator is as follows:
+@cindex @code{__has_include_next}
+
+The special operators @code{__has_include (@var{operand})} and
+@code{__has_include_next (@var{operand})} may be used in @samp{#if} and
+@samp{#elif} expressions to test whether the header referenced by their
+@var{operand} can be included using the @samp{#include} and
+@samp{#include_next} directive, respectively.  Using the operators in
+other contexts is not valid.  The @var{operand} takes the same form as
+the file in the @samp{#include} and @samp{#include_next} directives
+respectively (@pxref{Include Syntax}) and the operators evaluate to a
+nonzero value if the header can be included and to zero otherwise.  Note
+that that the ability to include a header doesn't imply that the header
+doesn't contain invalid constructs or @samp{#error} directives that
+would cause the preprocessor to fail.
+
+The @code{__has_include} and @code{__has_include_next} operators by
+themselves, without any @var{operand} or parentheses, act as
+predefined macros so that support for them can be tested in portable
+code.  Thus, the recommended use of the operators is as follows:
 
 @smallexample
 #if defined __has_include
@@ -3645,6 +3651,8 @@ but not with others that don't.
 #endif
 @end smallexample
 
+The same holds for @code{__has_include_next}.
+
 @node @code{__has_embed}
 @subsection @code{__has_embed}
 @cindex @code{__has_embed}