Ensure std is enabled in autocfg for round_ties_even probe

Author: bushrat011899

build.rs

@@ -4,6 +4,9 @@ fn main() {
 
     ac.emit_expression_cfg("1f64.total_cmp(&2f64)", "has_total_cmp"); // 1.62
     ac.emit_path_cfg("core::num::Saturating", "has_num_saturating"); // 1.74
+
+    // round_ties_even is only available in `std`
+    ac.set_no_std(false);
     ac.emit_expression_cfg("1.5f64.round_ties_even()", "has_round_ties_even"); // 1.77
 
     autocfg::rerun_path("build.rs");