Don't test for wxUSE_GSTREAMER in base-only Unix builds.

This avoids a -Wundef gcc warning as this symbol is not defined when the GUI
code is not built at all.
Use configure-generated setup.h for Android builds under Unix.

When using configure, building for Android is just a normal cross-build and
wx/setup.h, generated by configure, must be included, so don't include neither
wx/android/setup.h nor wx/android/config_android.h which don't work.

We need to set up include paths for Windows builds later so that
wx/android/setup.h is found first, ideally by copying it to lib/wx_android and
setting up the include paths so that this directory comes before include one.
Avoid inclusion of <algorithm> when wxUSE_STD_STRING==0.

Use wxUSE_STD_STRING as a proxy for "don't use standard library at all".

This allows to compile under Android with minimal/system C++ support.
Compilation fix wxSocket under Android.

Android/Bionic is unique in that it does have gethostbyname_r() but not
gethostbyaddr_r(), at least up to NDK r9d.

Work around this by testing for it explicitly here, in the future we should
either have a real configure test or, preferably, replace all this mess with
the use of getaddrinfo().