Enable embind in fastcomp/asm.js

With this change, embind supports asm.js/fastcomp.  To my knowledge, anyway.  :)  I have a little test program that works, but I have not tried to run the embind tests just yet, and we can't test against the IMVU code because we don't use fastcomp/asm.js yet.

One note: I applied @juj's patch to expose all the function tables as properties of the "asm" object.  It's a very minor issue, but I think it would be a little cleaner to expose a table of function tables as described in #2249 so the string concatenation is not necessary when looking up by signature.