Replace a few calls to intern with constant strings

Replace a few calls to intern with constant strings

* src/fns.c (do_yes_or_no_p, Fyes_or_no_p): Use symbol globals
rather than intern.
(syms_of_fns) <Qyes_or_no_p, Qy_or_n_p>: New symbols.

* src/lread.c (readevalloop): Use symbol global.
(syms_of_lread) <Qinternal_macroexpand_for_load>: New symbol.

(cherry picked from commit 8290a1bacb019f5026caa08334a7087802ebc6f9)