tests: Add a %abs_tmp substitution which is guaranteed to be a full path.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@81662 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/lit/TestRunner.py b/utils/lit/TestRunner.py
index 3e4b2c6..6ed3ce6 100644
--- a/utils/lit/TestRunner.py
+++ b/utils/lit/TestRunner.py
@@ -294,6 +294,8 @@
                           ('%S', os.path.dirname(sourcepath)),
                           ('%p', os.path.dirname(sourcepath)),
                           ('%t', tmpBase + '.tmp'),
+                          # FIXME: Remove this once we kill DejaGNU.
+                          ('%abs_tmp', tmpBase + '.tmp'),
                           ('#_MARKER_#', '%')])
 
     # Collect the test lines from the script.