www: Add note on running clang tests from a CMake build, patch  by Peter Collingbourne

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@105791 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/www/hacking.html b/www/hacking.html
index 3bbc0ea..07a0d6c 100644
--- a/www/hacking.html
+++ b/www/hacking.html
@@ -101,6 +101,9 @@
   <tt>make VERBOSE=1</tt> can be used to show more detail
   about what is being run.</p>
 
+  <p>If you built LLVM and Clang using CMake, the test suite can be run
+  with <tt>make clang-test</tt> from the top-level LLVM directory.</p>
+
   <p>The tests primarily consist of a test runner script running the compiler
   under test on individual test files grouped in the directories under the
   test directory.  The individual test files include comments at the