Currently the emscripten JavaScript environment for C/C++ programs
cannot do multithreading, and doesn't have a sysctl implementation
to get hardware CPU count. Hardcode to 1.
Using the Linux OS settings works, so not adding a platform file.
To build with emscripten (tested 1.30.0):
emmake make OS=emscripten ARCH=asmjs
The resulting libopenh264.so is LLVM bitcode which can be further
linked into an emscripten project for final JavaScript output.
