add libstdc++ package

programs that are cross-compiled will end up with a hardcoded
reference to the cross-compiler's libstdc++ library,
and that breaks usage of --with-sysroot, which has the result
of adding the sysroot path to all library paths returned by libtool.
therefore we must explicitly add libstdc++ to the deps, to ensure
that the native gcc/libstdc++.so is built, which does not have this
problem.
pango,libtiff: add libstdc++ as dep

this ensures that even in crosscompile scenarios the native host toolchain
is built and libtool files for the cross compiler's libstc++ don't get
in our way.
use --with-sysroot instead of "big hammer" to make libtool happy

background: I experienced libtool-related cross-compiling breakage
due to .la files returning paths pointing to the target rootfs instead
of picking paths from our -L flags, which would in a normal linkage scenario
pick the libraries installed in our x-compile "staging" directory.

the "big hammer", in our case simply rm'ing the offending libtool files,
had a nasty side-effect: library dependencies were not added automatically
anymore so we had to specify by them by *hand* for every single package.
this was a bad idea and would become a maintenance nightmare quickly.