extensions.xml: Add cross-reference.

	* doc/xml/manual/extensions.xml: Add cross-reference.
	* doc/html/manual/ext_compile_checks.html: Regenerate.

From-SVN: r222462

libstdc++-v3/ChangeLog

+2015-04-27  Jonathan Wakely  <jwakely@redhat.com>
+
+	* doc/xml/manual/extensions.xml: Add cross-reference.
+	* doc/html/manual/ext_compile_checks.html: Regenerate.
+
 2015-04-22  Szabolcs Nagy  <szabolcs.nagy@arm.com>
 
 	* config/os/generic/os_defines.h (_GLIBCXX_GTHREAD_USE_WEAK): Define.

libstdc++-v3/doc/html/manual/ext_compile_checks.html

@@ -29,7 +29,8 @@
       They can be enabled at configure time with
       <a class="link" href="configure.html" title="Configure"><code class="literal">--enable-concept-checks</code></a>.
       You can enable them on a per-translation-unit basis with
-      <code class="code">#define _GLIBCXX_CONCEPT_CHECKS</code> for GCC 3.4 and higher
+      <a class="link" href="using_macros.html" title="Macros"><code class="code">#define
+      _GLIBCXX_CONCEPT_CHECKS</code></a> for GCC 3.4 and higher
       (or with <code class="code">#define _GLIBCPP_CONCEPT_CHECKS</code> for versions
       3.1, 3.2 and 3.3).
    </p><p>Please note that the concept checks only validate the requirements

libstdc++-v3/doc/xml/manual/extensions.xml

@@ -82,7 +82,8 @@ extensions, be aware of two things:
       They can be enabled at configure time with
       <link linkend="manual.intro.setup.configure"><literal>--enable-concept-checks</literal></link>.
       You can enable them on a per-translation-unit basis with
-      <code>#define _GLIBCXX_CONCEPT_CHECKS</code> for GCC 3.4 and higher
+      <link linkend="manual.intro.using.macros"><code>#define
+      _GLIBCXX_CONCEPT_CHECKS</code></link> for GCC 3.4 and higher
       (or with <code>#define _GLIBCPP_CONCEPT_CHECKS</code> for versions
       3.1, 3.2 and 3.3).
    </para>