Add support for XFAILing valgrind runs with memory leak checking independently
of runs without leak checking.  We add -vg to the triple for non-checked runs,
or -vg_leak for checked runs.  Also use this to XFAIL the TableGen tests, since
tablegen leaks like a sieve.  This includes some valgrindArgs refactoring.

llvm-svn: 99103
diff --git a/llvm/test/TableGen/TreeNames.td b/llvm/test/TableGen/TreeNames.td
index 05a3298..ccdeb88 100644
--- a/llvm/test/TableGen/TreeNames.td
+++ b/llvm/test/TableGen/TreeNames.td
@@ -1,5 +1,6 @@
 // This tests to make sure we can parse tree patterns with names.
 // RUN: tblgen %s
+// XFAIL: vg_leak
 
 class TreeNode;
 class RegisterClass;