Merging r322901:

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r322901 | nico | 2018-01-18 13:40:27 -0800 (Thu, 18 Jan 2018) | 19 lines

Remove TautologicalInRangeCompare from Extra and TautologicalCompare.

This removes the following (already default-off) warnings from -Wextra:
  -Wtautological-type-limit-compare,
  -Wtautological-unsigned-zero-compare
  -Wtautological-unsigned-enum-zero-compare

On the thread "[cfe-dev] -Wtautological-constant-compare issues", clang
code owners Richard Smith, John McCall, and Reid Kleckner as well as
libc++ code owner Marshall Clow stated that these new warnings are not
yet ready for prime time and shouldn't be part of -Wextra.

Furthermore, Vedant Kumar (Apple), Peter Hosek (Fuchsia), and me (Chromium)
expressed the same concerns (Vedant on that thread, Peter on
https://reviews.llvm.org/D39462, me on https://reviews.llvm.org/D41512).

So remove them from -Wextra, and remove TautologicalInRangeCompare from
TautologicalCompare too until they're usable with real-world code.

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git-svn-id: https://llvm.org/svn/llvm-project/cfe/branches/release_60@322931 91177308-0d34-0410-b5e6-96231b3b80d8