tree.h: Declare folding_initializer.

tree.h: Declare folding_initializer.

gcc:

	* tree.h: Declare folding_initializer.
	* builtins.c (fold_builtin_constant_p): Give definite answer
	if folding inside an initializer.
	* fold-const.c: Define folding_initializer.
	(START_FOLD_INIT): Save and then set folding_initializer.
	(END_FOLD_INIT): Restore folding_initializer.

gcc/testsuite:

        * gcc.c-torture/compile/builtin_constant_p.c: New test.

From-SVN: r114358