[llvm] [docs] Add Included Suites to Test Suite Guide (PR #128937)

[Sam Elliott via llvm-commits]

https://github.com/lenary created https://github.com/llvm/llvm-project/pull/128937

This policy has never been written down, but was the intention when the GCC C Torture Suite was added.

In the years since that suite was added, individual changes to these tests have been landed, but we want to reject (or discourage) this going forwards, and look into reverting those changes.

>From c36f6381008ffe5d4adf628668fc437c490ee978 Mon Sep 17 00:00:00 2001
From: Sam Elliott <quic_aelliott at quicinc.com>
Date: Wed, 26 Feb 2025 11:25:29 -0800
Subject: [PATCH] [docs] Add Included Suites to Test Suite Guide

This policy has never been written down, but was the intention when the
GCC C Torture Suite was added.

In the years since that suite was added, changes to these tests have
been landed, but we want to reject (or discourage) this going forwards,
and look into reverting those changes.
---
 llvm/docs/TestSuiteGuide.md | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/llvm/docs/TestSuiteGuide.md b/llvm/docs/TestSuiteGuide.md
index aa8332ed8b7e1..93a5bd88fa278 100644
--- a/llvm/docs/TestSuiteGuide.md
+++ b/llvm/docs/TestSuiteGuide.md
@@ -352,6 +352,27 @@ performance. You can find more information at
 of the LLVM project is hosted at [http://lnt.llvm.org](http://lnt.llvm.org).
 
 
+Included Test Suites
+--------------------
+
+The LLVM Test Suite repository includes a number of test suites that we have
+copied into the repository from external sources, and hand-written CMake files
+to hook into the LLVM Test Suite system. For example, these include GCC's C
+and Fortran Torture test suites.
+
+In some cases, these external tests have a different license to other code in
+the llvm-test-suite repository, which must be documented in `LICENSE.TXT` in the
+root of the test suite repository, under the heading "Software from third
+parties included in the LLVM Project".
+
+The only changes we can accept to the tests in these suites are where we bring
+in all the changes from the external sources. Users should not make individual
+downstream changes to these tests.
+
+We do accept changes to the CMake integration files for these tests, and where a
+test is wrong/broken, we should have the ability to exclude the test from our
+integration with the suite.
+
 External Suites
 ---------------