[Tooling] Improve handling of CL-style options
This patch fixes the handling of clang-cl options in InterpolatingCompilationDatabase.
They were previously ignored completely, which led to a lot of bugs:
Additional options were being added with the wrong syntax. E.g. a file was
specified as C++ by adding -x c++, which causes an error in CL mode.
The args were parsed and then rendered, which means that the aliasing information
was lost. E.g. /W4 was rendered to -Wall, which in CL mode means -Weverything.
CL options were ignored when checking things like -std=, so a lot of logic was
Differential Revision: https://reviews.llvm.org/D51321