Update release notes for PR #5041

Author: ponylang-main

.release-notes/fix-tool-arch.md

@@ -12,3 +12,9 @@ The standard library is now always searched first, before any `--path` entries.
 
 If you were relying on `--path` to override a standard library package, that will no longer work.
 
+## Fix illegal instruction crashes in pony-lint, pony-lsp, and pony-doc
+
+The tool build commands didn't pass `--cpu` to ponyc, so ponyc targeted the build machine's specific CPU via `LLVMGetHostCPUName()`. Release builds happen on CI machines that often have newer CPUs than user machines. When a user ran pony-lint, pony-lsp, or pony-doc on an older CPU, the binary could contain instructions their CPU doesn't support, resulting in a SIGILL crash.
+
+The C/C++ side of the build already respected `PONY_ARCH` (e.g., `arch=x86-64` targets the baseline x86-64 instruction set). The Pony code generation for the tools just wasn't wired up to use it. Now it is.
+