[docs] Add clang release notes for LoongArch (#146481)

Author: Ami-zhang

clang/docs/ReleaseNotes.rst

@@ -985,6 +985,23 @@ Windows Support
 LoongArch Support
 ^^^^^^^^^^^^^^^^^
 
+- Add support for OHOS on loongarch64.
+
+- Add target attribute support for function. Supported formats include:
+  * `arch=<arch>` strings - specifies architecture features for a function (equivalent to `-march=<arch>`).
+  * `tune=<cpu>` strings - specifies the tune CPU for a function (equivalent to `-mtune`).
+  * `<feature>`/`no-<feature>` - enables/disables specific features.
+
+- Add support for the `_Float16` type. And fix incorrect ABI lowering of `_Float16`
+  in the case of structs containing fp16 that are eligible for passing via `GPR+FPR`
+  or `FPR+FPR`. Also fix `int16` -> `__fp16` conversion code gen, which uses generic LLVM
+  IR rather than `llvm.convert.to.fp16` intrinsics.
+
+- Add support for the `__bf16` type.
+
+- Fix incorrect _BitInt(N>64) alignment. Now consistently uses 16-byte alignment for all
+  `_BitInt(N)` where N > 64.
+
 RISC-V Support
 ^^^^^^^^^^^^^^