`OnlyStrict()` returns a match comparer for a single platform.
Unlike `Only()`, `OnlyStrict()` does not match sub platforms.
So, "arm/vN" will not match "arm/vM" where M < N, and "amd64" will not also match "386".
`OnlyStrict()` matches non-canonical forms. So, "arm64" matches "arm/64/v8".
Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>