libstdc++: Replace "Tunables" link with one that does not have an anchor

This works around a dblatex bug, where dblatex emits invalid TeX, by
placing a raw "#" in a \href.

Fixes: f6ff531d90 ("libstdc++: Update link to "Tunables" in Glibc manual")

libstdc++-v3/ChangeLog:

	* doc/xml/manual/using_exceptions.xml: Replace "Tunables" link
	with one that does not have an anchor.
	* doc/html/manual/using_exceptions.html: Regenerate.

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

@@ -366,7 +366,7 @@ is called.
       GCC Bug 25191: exception_defines.h #defines try/catch
 	</a>
       </em>. </span></p></div><div class="biblioentry"><a id="id-1.3.3.4.9.10.10"></a><p><span class="title"><em>
-	<a class="link" href="https://sourceware.org/glibc/manual/latest/html_mono/libc.html#Tunables" target="_top">
+	<a class="link" href="https://sourceware.org/glibc/manual/latest/html_node/Tunables.html" target="_top">
       Tunables, The GNU C Library
 	</a>
       </em>. </span></p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="using_concurrency.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="using.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="debug.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Concurrency </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Debugging Support</td></tr></table></div></body></html>

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

@@ -622,7 +622,7 @@ is called.
   <biblioentry>
       <title>
 	<link xmlns:xlink="http://www.w3.org/1999/xlink"
-	      xlink:href="https://sourceware.org/glibc/manual/latest/html_mono/libc.html#Tunables">
+	      xlink:href="https://sourceware.org/glibc/manual/latest/html_node/Tunables.html">
       Tunables, The GNU C Library
 	</link>
       </title>