Make a stub version of MITests, instead of reverting.

Lit tends to find out-of-date unittests in the build tree.

FIXME: It may be reverted several days after.
llvm-svn: 261194
diff --git a/llvm/unittests/MI/LiveIntervalTest.cpp b/llvm/unittests/MI/LiveIntervalTest.cpp
new file mode 100644
index 0000000..534bd0d
--- /dev/null
+++ b/llvm/unittests/MI/LiveIntervalTest.cpp
@@ -0,0 +1,6 @@
+#include "gtest/gtest.h"
+
+// FIXME: It may be removed when practical tests came.
+TEST(LiveIntervalTest, DummyStub) {
+  EXPECT_TRUE(true);
+}