Add NEWS.md entry for macro hygiene fix (JuliaLang#15850).

NEWS.md

@@ -220,6 +220,9 @@ This section lists changes that do not have deprecation warnings.
     `airybiprimex`, `airyaix`, `airybix`, `airyaiprimex`, `airybiprimex`)
     ([#18050]).
 
+  * When a macro is called in the module in which that macro is defined, global variables
+    in the macro are now correctly resolved in the macro definition environment ([#15850]).
+
   * `write` on an `IOBuffer` now returns a signed integer in order to be
     consistent with other buffers ([#20609]).
 
@@ -419,6 +422,7 @@ Deprecated or removed
 [#11310]: https://github.com/JuliaLang/julia/issues/11310
 [#12274]: https://github.com/JuliaLang/julia/issues/12274
 [#12563]: https://github.com/JuliaLang/julia/issues/12563
+[#15850]: https://github.com/JuliaLang/julia/issues/15850
 [#16213]: https://github.com/JuliaLang/julia/issues/16213
 [#16961]: https://github.com/JuliaLang/julia/issues/16961
 [#16984]: https://github.com/JuliaLang/julia/issues/16984