[ATFE] Update Changelog with recent additions and enhancements in 20.x. (arm#184)

Author: simpal01

arm-software/embedded/CHANGELOG.md

@@ -1,5 +1,34 @@
 # Changelog
 
 All notable changes to this project will be documented in this file.
+This release is migrated from [LLVM-ET](https://github.com/ARM-software/LLVM-embedded-toolchain-for-Arm).
+The package structure remains the same, making this a direct successor release.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
+
+## [20.1.0]
+
+### Added
+- Support for targeting AArch64 v8-R in both big-endian and little-endian modes (#64) (#68) (#102).
+- Additional library variants for AArch32 with strict alignment (LLVM-ET #605).
+- Support for targeting AArch32 M-profile in big-endian mode (#44) (#50) (#51) (LLVM-ET #626).
+- Support for targeting AArch32 A-profile in big-endian mode (#92) (#98).
+- Support for downloading AArch64 versions of FVPs (#73).
+- Newlib samples (#38).
+- Newlib-nano as multilib overlay package (#60).
+
+### Changed
+- AArch64 A-profile big endian library variants made strictly aligned (LLVM-ET #607).
+- Ensure sysroot is set when running libcxx tests (#57).
+- Enable exceptions/RTTI builds of libcxx with newlib (#36).
+- Disable debug symbols in picolibc builds (#135).
+- Handle meson test return code in picolibc tests (#162).
+- Reduce nesting of subproject build folders (#54).
+- Improve build efficiency by building library subprojects in parallel (#31).
+
+### Fixed
+- Store check-all results and continue libcxx tests on failure (#151).
+
+## [Old Releases]
+
+Previous release changelogs can be found [here](https://github.com/ARM-software/LLVM-embedded-toolchain-for-Arm/blob/llvm-19/CHANGELOG.md).