clang-cl: add support for the /? and /help options

This establishes a new Flag in Options.td, which can be assigned to
options that should be made available in clang's cl.exe compatible
mode, and updates the Driver to make use of the flag.

(The whitespace change to CMakeLists forces the build to re-run CMake
 and pick up the include dependency on the new .td file. This makes the
 build work if someone moves backwards in commit history after this change.)

Differential Revision: http://llvm-reviews.chandlerc.com/D1215

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187280 91177308-0d34-0410-b5e6-96231b3b80d8
Using the function pointer instead of the function type; this allows us to re-enable a warning in MSVC by default.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187292 91177308-0d34-0410-b5e6-96231b3b80d8
Fix formatting. No functional change.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187294 91177308-0d34-0410-b5e6-96231b3b80d8
Fix test/Driver/cl.c.

This test would fail in weird ways on systems with a one-letter filename
in the root directory, because the shell would helpfully expand /? to e.g. /n.

Make sure this doesn't happen by adding quotes.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187295 91177308-0d34-0410-b5e6-96231b3b80d8