Fix locating the 'lit.cfg' file when running on only a single file in the
current directory.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@78271 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/test/MultiTestRunner.py b/utils/test/MultiTestRunner.py
index 1da78dd..a48ba61 100755
--- a/utils/test/MultiTestRunner.py
+++ b/utils/test/MultiTestRunner.py
@@ -288,7 +288,8 @@
         if opts.config:
             opts.root = os.path.dirname(opts.config)
         else:
-            opts.root = os.path.commonprefix(inputs)
+            opts.root = os.path.commonprefix([os.path.abspath(p)
+                                              for p in inputs])
 
     # Find the config file, if not specified.
     if not opts.config: