clang-cl: parse (but don't support) the /o flag

Apparently folks run into this (PR17097). The flag is not supported by
MSVC either, but we should parse it so we don't get confused when it occurs.

This changes the clang-cl output for "clang-cl /c /o foo.obj" from:

  clang-cl.exe: error: no such file or directory: '/o'
  clang-cl.exe: error: no such file or directory: 'foo.obj'

to:

  clang-cl.exe: warning: argument unused during compilation: '/o bajs.obj'

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190323 91177308-0d34-0410-b5e6-96231b3b80d8
[docs] Typographical and rewording fixes.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190333 91177308-0d34-0410-b5e6-96231b3b80d8
[docs] Fix some finicky Sphinx warnings.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190336 91177308-0d34-0410-b5e6-96231b3b80d8
[docs] Fix Sphinx toctree warning.

Last I heard LSan is getting close to prime-time, but for now keep
LeakSanitizer.rst hidden (especially since it contains so little
content).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190337 91177308-0d34-0410-b5e6-96231b3b80d8
[docs] End users should see just "Clang"

Half the internet has wildly incorrect ideas about what LLVM is (in
particular, many get the impression that LLVM is some magical
cross-platform runtime), so saying "LLVM" near "cross-compilation" in a
user-facing doc might provoke confusion.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190338 91177308-0d34-0410-b5e6-96231b3b80d8