builtins.c (fold_builtin_signbit): Use build_zero_cst instead of fold_convert.

gcc/
	* builtins.c (fold_builtin_signbit): Use build_zero_cst instead of
	fold_convert.
	* c-typeck.c (build_function_call_vec): Likewise.
	* cfgexpand.c (expand_debug_expr): Likewise.
	* cgraphunit.c (assemble_thunk): Likewise.
	* config/sparc/sparc.c (sparc_fold_builtin): Likewise.
	* fold-const.c (fold_unary_loc, fold_mult_zconjz): Likewise.
	(fold_binary_loc, fold_ternary_loc): Likewise.
	* gimple-fold.c (get_symbol_constant_value): Likewise.
	* gimple-low.c (lower_builtin_setjmp): Likewise.
	* gimple.c (gimple_cond_get_ops_from_tree): Likewise.
	* gimplify.c (gimplify_init_constructor): Likewise.
	* lambda.h (build_linear_expr): Likewise.
	* omp-low.c (omp_reduction_init): Likewise.
	* tree-inline.c (remap_ssa_name): Likewise.
	* tree-object-size.c (compute_object_sizes): Likewise.
	* tree-sra.c (init_subtree_with_zero): Likewise.
	(sra_ipa_modify_assign): Likewise.
	* tree-ssa-copy.c (propagate_tree_value_into_stmt): Likewise.
	* tree-ssa-reassoc.c (eliminate_duplicate_pair): Likewise.
	(eliminate_plus_minus_pair, eliminate_not_pairs): Likewise.
	(undistribute_ops_list): Likewise.
	* tree-ssa-sccvn.c (vn_reference_lookup_3): Likewise.
	* tree-vect-stmts.c (vectorizable_call): Likewise.
	* tree.c (build_vector_from_ctor, build_one_cst): Likewise.
	(build_zero_cst): Handle more cases directly.  Update comment.

gcc/cp/
	* class.c (build_base_path, add_vcall_offset): Use build_zero_cst
	instead of fold_convert.
	* init.c (build_zero_init): Likewise.
	* typeck.c (cp_build_binary_op): Likewise.

gcc/fortran/
	* trans-decl.c (add_argument_checking): Use build_zero_cst instead of
	fold_convert.
	* trans-expr.c (gfc_conv_missing_dummy, fill_with_spaces): Likewise.
	* trans-stmt.c (gfc_trans_do): Likewise.

From-SVN: r166227