Changelog: Add entry for --enable-executable-static

Author: nh2

Cabal/ChangeLog.md

@@ -1,4 +1,13 @@
 # 2.4.0.0 (current development version)
+  * Static linking
+    * Add `--enable-executable-static` flag for building fully
+      static executables (GHC's normal "statish" linking links
+      Haskell libraries statically, but libc and system dependencies
+      dynamically). This new flag links everything statically.
+    * Note you likely want to link against `musl` or another libc that
+      supports fully static linking;
+      [`glibc` has some issues](https://sourceware.org/glibc/wiki/FAQ#Even_statically_linked_programs_need_some_shared_libraries_which_is_not_acceptable_for_me.__What_can_I_do.3F)
+      with fully static linking.
   * Add `readGhcEnvironmentFile` to parse GHC environment files.
   * Drop support for GHC 7.4, since it is out of our support window
     (and has been for over a year!)