Ensure that constant folding runs with IN_PERL_RUNTIME true, by copying

the current compiling cop to a different address. This ensures that
lexical hints are correctly honoured, and allows us to fold sprintf.

p4raw-id: //depot/perl@33369

op.c

@@ -2428,6 +2428,7 @@ Perl_fold_constants(pTHX_ register OP *o)
     OP *old_next;
     SV * const oldwarnhook = PL_warnhook;
     SV * const olddiehook  = PL_diehook;
+    COP not_compiling;
     dJMPENV;
 
     PERL_ARGS_ASSERT_FOLD_CONSTANTS;
@@ -2492,6 +2493,13 @@ Perl_fold_constants(pTHX_ register OP *o)
     oldscope = PL_scopestack_ix;
     create_eval_scope(G_FAKINGEVAL);
 
+    /* Verify that we don't need to save it:  */
+    assert(PL_curcop == &PL_compiling);
+    StructCopy(&PL_compiling, &not_compiling, COP);
+    PL_curcop = &not_compiling;
+    /* The above ensures that we run with all the correct hints of the
+       currently compiling COP, but that IN_PERL_RUNTIME is not true. */
+    assert(IN_PERL_RUNTIME);
     PL_warnhook = PERL_WARNHOOK_FATAL;
     PL_diehook  = NULL;
     JMPENV_PUSH(ret);
@@ -2525,6 +2533,7 @@ Perl_fold_constants(pTHX_ register OP *o)
     JMPENV_POP;
     PL_warnhook = oldwarnhook;
     PL_diehook  = olddiehook;
+    PL_curcop = &PL_compiling;
 
     if (PL_scopestack_ix > oldscope)
 	delete_eval_scope();

opcode.h

@@ -1667,7 +1667,7 @@ EXTCONST U32 PL_opargs[] = {
 	0x0022281c,	/* vec */
 	0x0122291c,	/* index */
 	0x0122291c,	/* rindex */
-	0x0004280d,	/* sprintf */
+	0x0004280f,	/* sprintf */
 	0x00042805,	/* formline */
 	0x0001379e,	/* ord */
 	0x0001378e,	/* chr */

opcode.pl

@@ -773,7 +773,7 @@ sub tab {
 index		index			ck_index	isT@	S S S?
 rindex		rindex			ck_index	isT@	S S S?
 
-sprintf		sprintf			ck_fun		mst@	S L
+sprintf		sprintf			ck_fun		fmst@	S L
 formline	formline		ck_fun		ms@	S L
 ord		ord			ck_fun		ifsTu%	S?
 chr		chr			ck_fun		fsTu%	S?