Revert "Temporarily revert CV-in-stash optimisation"

This reverts commit 6eed25e.

op.c

@@ -9617,7 +9617,7 @@ Perl_newATTRSUB_x(pTHX_ I32 floor, OP *o, OP *proto, OP *attrs,
 	   sub is stored in.  */
 	const I32 flags =
 	   ec ? GV_NOADD_NOINIT
-	      :   PL_curstash != CopSTASH(PL_curcop)
+	      :   (IN_PERL_RUNTIME && PL_curstash != CopSTASH(PL_curcop))
 	       || memchr(name, ':', namlen) || memchr(name, '\'', namlen)
 		    ? gv_fetch_flags
 		    : GV_ADDMULTI | GV_NOINIT | GV_NOTQUAL;

t/op/sub.t

@@ -423,7 +423,6 @@ is ref($main::{rt_129916}), 'CODE', 'simple sub stored as CV in stash (main::)';
     sub foo { 42 }
 }
 {
-    local $TODO = "CV symbol table optimization only works in main:: [perl #129916]";
     is ref($RT129916::{foo}), 'CODE', 'simple sub stored as CV in stash (non-main::)';
 }