experimental patch to simplify generated function detection
disable test_openjpeg in s_x_x
send only a marker of generated functions to js-optimizer.js; we either know the generated functions and send only them, or we don't know them and send all the code, in either case js-optimizer.js does not need a list of generated functions
deprecate USE_TYPED_ARRAYS=1 and QUANTUM_SIZE=1
run registerize pass last
make sure we use a C compiler to build libc. fixes #937, #938
Update to current libcxx.

This doesn't work yet as it needs to be customized for use with
emscripten still.
Get things working with the new libcxx / libcxxabi.