emsdk

Update CMAKE_OSX_DEPLOYMENT_TARGET from 10.11 to 10.14 (#924)

Apparently 10.11 is no longer good enough to run the latest version of
binaryen.  Specifically since binaryen switched to using std::variant it
now fails to build with this set to 10.11.

This is also the version used on the emscripten-releases CI which builds
the emsdk binaries:
https://chromium.googlesource.com/emscripten-releases/+/refs/heads/main/src/build.py#673