Define c_fully_fold separately for C and C++.

Define c_fully_fold separately for C and C++.

gcc/c-family/
	* c-common.c (c_disable_warnings, c_enable_warnings, c_fully_fold)
	(c_fully_fold_internal, decl_constant_value_for_optimization):
	Move to c/c-fold.c.
	* c-common.h: Don't declare decl_constant_value_for_optimization.
gcc/c/
	* c-fold.c (c_disable_warnings, c_enable_warnings, c_fully_fold)
	(c_fully_fold_internal, decl_constant_value_for_optimization):
	Move from c-common.c.
	* c-tree.h: Declare decl_constant_value_for_optimization.
	* Make-lang.in (C_AND_OBJC_OBJS): Add c-fold.o.
gcc/cp/
	* cp-gimplify.c (c_fully_fold): Define.

From-SVN: r231196