[ArgumentPromotion] Add a lit.local.cfg to disable X86 specific tests if the X86 target doesn't exist.

Hopefully this fixes some buildbot failure after r354376

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354388 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Transforms/ArgumentPromotion/X86/lit.local.cfg b/test/Transforms/ArgumentPromotion/X86/lit.local.cfg
new file mode 100644
index 0000000..e71f3cc
--- /dev/null
+++ b/test/Transforms/ArgumentPromotion/X86/lit.local.cfg
@@ -0,0 +1,3 @@
+if not 'X86' in config.root.targets:
+    config.unsupported = True
+