[llvm] Introduce llvmremark util diff command (PR #85007)

[Jessica Paquette via llvm-commits]

================
@@ -425,3 +427,144 @@ EXIT STATUS
 
 :program:`llvm-remarkutil size-diff` returns 0 on success, and a non-zero value
 otherwise.
+
+.. _diff_subcommand:
+
+diff
+~~~~~
+
+.. program:: llvm-remarkutil diff
+
+
+USAGE: :program:`llvm-remarkutil diff` [*options*] <remarka_file>  <remarkb_file>
+
+Summary
+^^^^^^^
+
+:program:`llvm-remarkutil diff` hilights the difference between two versions of `remarks <https://llvm.org/docs/Remarks.html>`_ based on specified properties.
+The tool will organise remarks based on the debug location and highlight the differences between remarks with the same header i.e remark name, pass name and function name. The tool by default highlights the differences in arguments between two remarks and the difference in remark type.
----------------
ornata wrote:

> The tool will organise remarks based on the debug location and highlight the differences between remarks with the same header i.e remark name, pass name and function name

How about

> The tool will highlight differences in remarks with the same remark name, pass name, and function name. Remarks are sorted by debug location.

https://github.com/llvm/llvm-project/pull/85007