(syntax-check): Move each individual check into its own target.

(syntax-check): Move each individual check into its own target.
(syntax-check-rules): This is the list of syntax-check targets.
(sc_unmarked_diagnostics, sc_cast_of_argument_to_free):
(sc_cast_of_x_alloc_return_value, sc_space_tab):
(sc_error_exit_success, sc_xalloc_h_in_src):  New targets.