Finalize changelog for v1.43.0 (#5276)

Author: kinke

CHANGELOG.md

@@ -1,5 +1,13 @@
 # LDC master
 
+#### Big news
+
+#### Platform support
+
+#### Bug fixes
+
+# LDC 1.43.0 (2026-08-30)
+
 #### Big news
 - Frontend, druntime and Phobos are at version [2.113.0](https://dlang.org/changelog/2.113.0.html), incl. new command-line option `-foptimize-nothrow` to restore the `nothrow` optimizations. (#5113, #5221, #5239, #5273)
   - `-foptimize-nothrow` is the default setting when targeting Windows or WebAssembly, to make hitting https://github.com/ldc-developers/ldc/issues/3504 much less likely.