Make lit.site.cfg Py3-compatible. Copied from r188041.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@198204 91177308-0d34-0410-b5e6-96231b3b80d8

test/lit.site.cfg.in

@@ -1,3 +1,5 @@
+import sys
+
 ## Autogenerated by LLVM/Clang configuration.
 # Do not edit!
 config.llvm_src_root = "@LLVM_SOURCE_DIR@"
@@ -14,7 +16,8 @@ config.have_libedit = "@HAVE_LIBEDIT@"
 try:
     config.llvm_tools_dir = config.llvm_tools_dir % lit_config.params
     config.llvm_libs_dir = config.llvm_libs_dir % lit_config.params
-except KeyError,e:
+except KeyError:
+    e = sys.exc_info()[1]
     key, = e.args
     lit_config.fatal("unable to find %r parameter, use '--param=%s=VALUE'" % (key,key))