Oh, I see. No, not yet, I think the C compilers are complex enough to be difficult to compile with emscripten. I have no evidence for that, but I know they are incredibly complex.
The shorter path is something like LLVM, but we could see something like a compiler all in js that can take a large subset of C and compile it.
EDIT: see azakai's comment below which provides much better insight into this
The ideal solution would be an editor (like codemirror or ace) with a compile+run button that would compile the code down to JS and run it.