[Bash-autocompletion] Pass all flags in shell command-line to Clang

Previously, we passed "#" to --autocomplete to indicate to enable cc1
flags. For example, when -cc1 or -Xclang was passed to bash, bash
executed `clang --autocomplete=#-<flag they want to complete>`.

However, this was not a good implementation because it depends -Xclang
and -cc1 parsing to shell. So I changed this to pass all flags shell
has, so that Clang can handle them internally.

I had to change many testcases because API spec changed quite a lot.

Reviewers: teemperor, v.g.vassilev

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D39342

llvm-svn: 326684