Small speed improvement for JITed lisp function dispatch

Small speed improvement for JITed lisp function dispatch

* src/alloc.c (make-byte-code):
* src/bytecode-jit.c (jit_byte_code__):
* src/bytecode.c [HAVE_LIBJIT] (exec_byte_code):
* src/eval.c (funcall_lambda):
* src/lisp.h (funcall_lambda): Store pointer to bytecode execution function
(either `exec_byte_code' or `jit_exec') in Lisp_Compiled objects to avoid
the need for an extra function call in `exec_byte_code'.