[libc++] [CI] Fail if the headers contain cyclic dependencies.

Since we have a tool to detect cycles now; and since we're entering
a phase where people can easily introduce cycles by accident (D100682)
or by request (D90999), I think it's increasingly important to shift
the burden of detecting these cycles onto the buildbot instead of
the poor human reviewer.

Also, grep for non-ASCII characters (such as U+200B and U+00AD)
and hard tabs; don't let those get checked in.

Differential Review: https://reviews.llvm.org/D100703