Change layering warning tests to not actually build modules.

Specifically, we want to warn only for direct layering violations for
the modules we are calling clang on.

This temporarily unblocks
http://llvm-reviews.chandlerc.com/D2374

Once that is in, we'll also want to investigate whether to check the
layering in the build step of modules that we build transitively.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@197021 91177308-0d34-0410-b5e6-96231b3b80d8
Mention LeakSanitizer in AddressSanitizer docs.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@197022 91177308-0d34-0410-b5e6-96231b3b80d8
Turning IAS on by default on ARM/Thumb

This is an experimental feature, where -integrated-as will be
on by default on ARM/Thumb. We aim to detect the missing features
so that the next release is stable.

Updating the ReleaseNotes, too.

Also moving the AArch64 into the same place.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@197024 91177308-0d34-0410-b5e6-96231b3b80d8