function lookupCompiler(compiler) {
	if ('function' === typeof compiler) return compiler;
	switch (compiler) {
		case 'coffeescript':
		case 'coffee-script':
		case 'cs':
		case 'text/coffeescript':
			return getCoffeeScriptCompiler();
		case 'javascript':
		case 'java-script':
		case 'js':
		case 'text/javascript':
			return jsCompiler;
		default:
			throw new VMError(`Unsupported compiler '${compiler}'.`);
	}
}
Look up the compiler for a specific name.

@private
@param {(string|compileCallback)} compiler - A compile callback or the name of the compiler.
@return {compileCallback} The resolved compiler.
@throws {VMError} If the compiler is unknown or the coffee script module was needed and couldn't be found.