riscv: Fix up riscv_atomic_assign_expand_fenv [PR94950]

Similarly to the fixes on many other targets, riscv needs to use TARGET_EXPR
to avoid having the create_tmp_var_raw temporaries without proper DECL_CONTEXT
and not mentioned in local decls.

2020-05-06  Jakub Jelinek  <jakub@redhat.com>

	PR target/94950
	* config/riscv/riscv-builtins.c (riscv_atomic_assign_expand_fenv): Use
	TARGET_EXPR instead of MODIFY_EXPR for first assignment to old_flags.

gcc/ChangeLog

 2020-05-06  Jakub Jelinek  <jakub@redhat.com>
 
+	PR target/94950
+	* config/riscv/riscv-builtins.c (riscv_atomic_assign_expand_fenv): Use
+	TARGET_EXPR instead of MODIFY_EXPR for first assignment to old_flags.
+
+2020-05-06  Jakub Jelinek  <jakub@redhat.com>
+
 	PR rtl-optimization/94873
 	* combine.c (combine_instructions): Don't optimize using REG_EQUAL
 	note if SET_SRC (set) has side-effects.

gcc/config/riscv/riscv-builtins.c

@@ -283,8 +283,8 @@ riscv_atomic_assign_expand_fenv (tree *hold, tree *clear, tree *update)
   tree fsflags = GET_BUILTIN_DECL (CODE_FOR_riscv_fsflags);
   tree old_flags = create_tmp_var_raw (RISCV_ATYPE_USI);
 
-  *hold = build2 (MODIFY_EXPR, RISCV_ATYPE_USI, old_flags,
-		  build_call_expr (frflags, 0));
+  *hold = build4 (TARGET_EXPR, RISCV_ATYPE_USI, old_flags,
+		  build_call_expr (frflags, 0), NULL_TREE, NULL_TREE);
   *clear = build_call_expr (fsflags, 1, old_flags);
   *update = NULL_TREE;
 }