(1) Add ".test" to test/Other/lit.local.cfg, so llvm-cov.test is actually run.
(2) Rename llvm-cov test inputs so the string "llvm-cov" doesn't get
substituted by lit within the input filenames on the RUN line.
(3) XFAIL llvm-cov.test because it asserts:
include/llvm/ADT/SmallVector.h:140: reference llvm::SmallVectorTemplateCommon<llvm::GCOVBlock *, void>::operator[](unsigned int) [T = llvm::GCOVBlock *]: Assertion `begin() + idx < end()' failed.