[lit] Print substitutions with --show-suites
We already print available features, and it can be useful to print
substitutions as well since those are a pretty fundamental part of
a test suite. We could also consider printing other things like the
test environment, however the need doesn't appear to be as strong.
As a fly-by fix, we also always print available features, even when
there are none.
Before:
$ lit -sv libcxx/test --show-suites
-- Test Suites --
libc++ - 6350 tests
Source Root: [...]
Exec Root : [...]
Available Features : -faligned-allocation -fsized-deallocation [...]
After:
$ lit -sv libcxx/test --show-suites
-- Test Suites --
libc++ - 6350 tests
Source Root: [...]
Exec Root : [...]
Available Features: -faligned-allocation -fsized-deallocation [...]
Available Substitutions: %{build_module} => [...]
%{build} => %{cxx} -o [...]
Differential Revision: https://reviews.llvm.org/D77818