ci: Add nightly CI job for clang++ with NMake

In commit c1f4bd79 (ci: Add LLVM/Clang 13.0 nightly CI jobs on
Windows, 2022-02-02) we added three of the four combinations of
`clang-cl`/`clang++` with NMake/Ninja.  Add the last combination.
30 jobs for !6961 with ci-clang-windows in 5 minutes and 55 seconds (queued for 2 seconds)
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