title: Compile cln with clang and libc++
body: <p>I try to compile cln with clang and libc++ linked as my project, which uses ginac (which itself uses cln) requires certain c++11 features. During my attempts I found out, that linking against libc++ instead of stdlibc++ should do the trick, so I ended up in using the following command to configure:</p>
  
  <pre><code>./configure CXX=/usr/bin/clang++ CXXFLAGS="-stdlib=libc++ -std=c++11" LDFLAGS="-stdlib=libc++"
  </code></pre>
  
  <p>which works fine. However I get the following error messages upon invoking make:</p>
  
  <pre><code>Making all in src
  /bin/sh ../libtool  --tag=CXX   --mode=compile /usr/bin/clang++ -DHAVE_CONFIG_H -I. -    I../autoconf  -I../include -I../src -I../include -I../src   -stdlib=libc++ -std=c++11 -MT   cl_alloca.lo -MD -MP -MF .deps/cl_alloca.Tpo -c -o cl_alloca.lo `test -f 'base/cl_alloca.cc'  || echo './'`base/cl_alloca.cc
  libtool: compile:  /usr/bin/clang++ -DHAVE_CONFIG_H -I. -I../autoconf -I../include -   I../src -I../include -I../src -stdlib=libc++ -std=c++11 -MT cl_alloca.lo -MD -MP -MF .deps/cl_alloca.Tpo -c base/cl_alloca.cc  -fno-common -DPIC -o .libs/cl_alloca.o
  In file included from base/cl_alloca.cc:4:
  In file included from ./base/cl_sysdep.h:56:
  In file included from ./base/cl_macros.h:7:
  ../include/cln/exception.h:14:24: error: implicit instantiation of undefined template     'std::__1::basic_string&lt;char, std::__1::char_traits&lt;char&gt;, std::__1::allocator&lt;char&gt; &gt;'
              : std::runtime_error(std::string()) {}
                                   ^
  /usr/bin/../lib/c++/v1/iosfwd:187:28: note: template is declared here
      class _LIBCPP_TYPE_VIS basic_string;
                         ^
  1 error generated.
  make[1]: *** [cl_alloca.lo] Error 1
  make: *** [all-recursive] Error 1
  </code></pre>
  
  <p>What am I doing wrong and how can I interpret this errormessage and finally fix my problem?</p>