Change libcxx SKIPPED to FAIL when MSVC ships P0960

[CaseyCarter]

MSVC has implemented (but not yet shipped) support for P0960R3 "Allow initializing aggregates from a parenthesized list of values". The libcxx test std/utilities/tuple/tuple.tuple/tuple.creation/tuple_cat.pass.cpp is broken by this C++20 feature, so we recently SKIPPED it in tests/libcxx/expected_results.txt and tests/libcxx/skipped_tests.txt. Once VS 2019 v 16.8p3 ships - which is expected to include the P0960 support - we should change the SKIPPED in tests/libcxx/expected_results.txt to an expected failure for MSVC only which IIRC corresponds to:

 # *** CLANG FEATURES NOT YET IMPLEMENTED ***
 # P0960R3 "Allow initializing aggregates from a parenthesized list of values"
-std/utilities/tuple/tuple.tuple/tuple.creation/tuple_cat.pass.cpp SKIPPED # TRANSITION, VS 2019 16.8 p3
+std/utilities/tuple/tuple.tuple/tuple.creation/tuple_cat.pass.cpp:0 FAIL

(A better fix would be to fix this test upstream and remove the skips, but we're currently blocked from updating LLVM due to LIT changes; see #1090.)