Executables that use libbullet are now 1 MiB smaller (stripped!).

The only reason we had to keep this was for emscripten builds. We can
now use SDL v2 using “emconfigure ./configure CFLAGS="-s USE_SDL=2” and
a few additional flags.

SDL_Mixer v2 is not available in emscripten packages but either it will
be added at some time, or I will get rid of it altogether. An alternate
solution could be this code snippet I found:

    cd SDL2_mixer
    emconfigure ./configure --prefix=$(pwd)/dist --enable-music-ogg --disable-music-ogg-shared CFLAGS="-s USE_VORBIS=1"
    emmake make install

Since C++11 threads are available on every platform that has threads, we
no longer need our pthread implementation. The LOL_FEATURE_CXX11_THREADS
macro is gone, too, and we now just use LOL_FEATURE_THREADS.

Note that it is still necessary to link with -lpthread or -pthread on
some platforms, so we don’t throw that part away.

MeshViewer first pass

optimisation flag -Os instead of -O3.

a bug in emcc that won’t let us discover SDL.h.

no known regressions yet.

memory leak in OS X llvm-g++.

to external so as to avoid some autocompletion collisions with "configure".

before it also runs on Linux or OS X.

the C compiler (the Android build script did that).

but we can now create shared objects for each project; only the testsuite
is not building properly because of issues with STLport, and EglApp is
deactivated because AndroidApp should have precedence.

parallel builds accordingly.

appear shorter on the web page.

fail the build (if eg. we try to build an amd64 binary on i386).

g++ understands -lcaca directly; also add -DCACA_STATIC to the default flags.