libstdc++: Use LTLIBICONV when linking libstdc++.so [PR93602]

This fixes missing libiconv symbols when libstdc++ is built on a system
that has libiconv installed. If the libiconv headers are found then
libstdc++ depends on libiconv_open etc instead of libc's iconv_open. But
without this fix libstdc++ is not linked to the libiconv library that
provides the definitions of those symbols.

As discussed in PR 93602 this changed means that libstdc++.so.6 might
have an rpath pointing to the location of the libiconv.so library. If
that is not desired, then GCC must be configured to link to a static
libiconv.a instead, using either --with-libiconv-type=static or an
in-tree build of libiconv.

libstdc++-v3/ChangeLog:

	PR libstdc++/93602
	* doc/xml/manual/prerequisites.xml: Document libiconv
	workarounds.
	* doc/html/manual/setup.html: Regenerate.
	* src/Makefile.am (CXXLINK): Add $(LTLIBICONV).
	* src/Makefile.in: Regenerate.

4 files changed, 89 insertions, 2 deletions

diff --git a/libstdc++-v3/doc/html/manual/setup.html b/libstdc++-v3/doc/html/manual/setup.html
index 636a440..069354b 100644
--- a/libstdc++-v3/doc/html/manual/setup.html
+++ b/libstdc++-v3/doc/html/manual/setup.html
@@ -42,6 +42,39 @@
    </p><p>
    Finally, a few system-specific requirements:
    </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">linux</span></dt><dd><p>
+	  The 'gnu' locale model makes use of <code class="function">iconv</code>
+	  for character set conversions. The relevant functions are provided
+	  by Glibc and so are always available, however they can also be
+	  provided by the separate GNU libiconv library. If GNU libiconv is
+	  found when GCC is built (e.g., because its headers are installed
+	  in <code class="filename">/usr/local/include</code>)
+	  then the <code class="filename">libstdc++.so.6</code> library will have a
+	  run-time dependency on <code class="filename">libiconv.so.2</code>.
+	  If you do not want that run-time dependency then you should do
+	  one of the following:
+	</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
+	      Uninstall the libiconv headers before building GCC.
+	      Glibc already provides <code class="function">iconv</code> so you should
+	      not need libiconv anyway.
+	    </p></li><li class="listitem"><p>
+	    <a class="link" href="../">
+	    Download</a> the libiconv sources and extract them into the
+	    top level of the GCC source tree, e.g.,
+	    </p><pre class="programlisting">
+wget https://ftp.gnu.org/pub/gnu/libiconv/libiconv-1.16.tar.gz
+tar xf libiconv-1.16.tar.gz
+ln -s libiconv-1.16 libiconv
+</pre><p>
+	      This will build libiconv as part of building GCC and link to
+	      it statically, so there is no <code class="filename">libiconv.so.2</code>
+	      dependency.
+	    </p></li><li class="listitem"><p>
+	      Configure GCC with <code class="option">--with-libiconv-type=static</code>.
+	      This requires the static <code class="filename">libiconv.a</code> library,
+	      which is not installed by default. You might need to reinstall
+	      libiconv using the <code class="option">--enable-static</code> configure
+	      option to get the static library.
+	    </p></li></ul></div><p>
 	  If GCC 3.1.0 or later on is being used on GNU/Linux, an attempt
 	  will be made to use "C" library functionality necessary for
 	  C++ named locale support.  For GCC 4.6.0 and later, this
diff --git a/libstdc++-v3/doc/xml/manual/prerequisites.xml b/libstdc++-v3/doc/xml/manual/prerequisites.xml
index 22e90a7..8799487 100644
--- a/libstdc++-v3/doc/xml/manual/prerequisites.xml
+++ b/libstdc++-v3/doc/xml/manual/prerequisites.xml
@@ -50,6 +50,56 @@
 
 	<listitem>
 	<para>
+	  The 'gnu' locale model makes use of <function>iconv</function>
+	  for character set conversions. The relevant functions are provided
+	  by Glibc and so are always available, however they can also be
+	  provided by the separate GNU libiconv library. If GNU libiconv is
+	  found when GCC is built (e.g., because its headers are installed
+	  in <filename class="directory">/usr/local/include</filename>)
+	  then the <filename>libstdc++.so.6</filename> library will have a
+	  run-time dependency on <filename>libiconv.so.2</filename>.
+	  If you do not want that run-time dependency then you should do
+	  one of the following:
+	</para>
+	<itemizedlist>
+	  <listitem>
+	    <para>
+	      Uninstall the libiconv headers before building GCC.
+	      Glibc already provides <function>iconv</function> so you should
+	      not need libiconv anyway.
+	    </para>
+	  </listitem>
+	  <listitem>
+	    <para>
+	    <link linkend="https://www.gnu.org/software/libiconv/#downloading">
+	    Download</link> the libiconv sources and extract them into the
+	    top level of the GCC source tree, e.g.,
+	    </para>
+<programlisting>
+wget https://ftp.gnu.org/pub/gnu/libiconv/libiconv-1.16.tar.gz
+tar xf libiconv-1.16.tar.gz
+ln -s libiconv-1.16 libiconv
+</programlisting>
+	    <para>
+	      This will build libiconv as part of building GCC and link to
+	      it statically, so there is no <filename>libiconv.so.2</filename>
+	      dependency.
+	    </para>
+	  </listitem>
+	  <listitem>
+	    <para>
+	      Configure GCC with <option>--with-libiconv-type=static</option>.
+	      This requires the static <filename>libiconv.a</filename> library,
+	      which is not installed by default. You might need to reinstall
+	      libiconv using the <option>--enable-static</option> configure
+	      option to get the static library.
+	    </para>
+	  </listitem>
+	</itemizedlist>
+	</listitem>
+
+	<listitem>
+	<para>
 	  If GCC 3.1.0 or later on is being used on GNU/Linux, an attempt
 	  will be made to use "C" library functionality necessary for
 	  C++ named locale support.  For GCC 4.6.0 and later, this
diff --git a/libstdc++-v3/src/Makefile.am b/libstdc++-v3/src/Makefile.am
index 18f5763..9c3f4ac 100644
--- a/libstdc++-v3/src/Makefile.am
+++ b/libstdc++-v3/src/Makefile.am
@@ -278,7 +278,9 @@ CXXLINK = \
 	$(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) \
 	--mode=link $(CXX) \
 	$(VTV_CXXLINKFLAGS) \
-	$(OPT_LDFLAGS) $(SECTION_LDFLAGS) $(AM_CXXFLAGS) $(LTLDFLAGS) -o $@
+	$(OPT_LDFLAGS) $(SECTION_LDFLAGS) $(AM_CXXFLAGS) \
+	$(LTLDFLAGS) $(LTLIBICONV) \
+	-o $@
 
 # Symbol versioning for shared libraries.
 if ENABLE_SYMVERS
diff --git a/libstdc++-v3/src/Makefile.in b/libstdc++-v3/src/Makefile.in
index eeafb89..4a06f6c 100644
--- a/libstdc++-v3/src/Makefile.in
+++ b/libstdc++-v3/src/Makefile.in
@@ -643,7 +643,9 @@ CXXLINK = \
 	$(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) \
 	--mode=link $(CXX) \
 	$(VTV_CXXLINKFLAGS) \
-	$(OPT_LDFLAGS) $(SECTION_LDFLAGS) $(AM_CXXFLAGS) $(LTLDFLAGS) -o $@
+	$(OPT_LDFLAGS) $(SECTION_LDFLAGS) $(AM_CXXFLAGS) \
+	$(LTLDFLAGS) $(LTLIBICONV) \
+	-o $@
 
 @ENABLE_SYMVERS_TRUE@CLEANFILES = libstdc++-symbols.ver $(version_dep)
 @ENABLE_SYMVERS_DARWIN_TRUE@@ENABLE_SYMVERS_TRUE@version_arg = -Wl,-exported_symbols_list,libstdc++-symbols.explist