Rollup merge of #78425 - chansuke:move_nan, r=jyn514

Move f64::NAN ui tests into `library`

This is a partial fix of #76268.

r? ```@matklad```

library/core/tests/num/mod.rs

@@ -27,6 +27,8 @@
 mod dec2flt;
 mod flt2dec;
 
+mod nan;
+
 /// Adds the attribute to all items in the block.
 macro_rules! cfg_block {
     ($(#[$attr:meta]{$($it:item)*})*) => {$($(

library/core/tests/num/nan.rs

@@ -1,7 +1,6 @@
-// run-pass
-
-pub fn main() {
-    use std::f64;
+#[test]
+fn test_nan() {
+    use core::f64;
     let x = "NaN".to_string();
     assert_eq!(format!("{}", f64::NAN), x);
     assert_eq!(format!("{:e}", f64::NAN), x);