Finalize changelog for v1.40.0

Author: kinke

CHANGELOG.md

@@ -1,5 +1,13 @@
 # LDC master
 
+#### Big news
+
+#### Platform support
+
+#### Bug fixes
+
+# LDC 1.40.0 (2024-12-15)
+
 #### Big news
 - Frontend, druntime and Phobos are at version [2.110.0](https://dlang.org/changelog/2.110.0.html). (#4707, #4737, #4749, #4768, #4784, #4792, #4798)
 - Support for [LLVM 19](https://releases.llvm.org/19.1.0/docs/ReleaseNotes.html). The prebuilt packages use v19.1.3 (incl. macOS arm64). (#4712, #4735, #4763, #4772)