Recommit r329442: Generate Libclang invocation reproducers using a new

Recommit r329442: Generate Libclang invocation reproducers using a new
-cc1gen-reproducer driver option

The recommit fixes:
- An MSAN failure (CCPrintOptions wasn't initialized in the Driver)
- Ensures that the strings in the libclang invocation files are escaped

Original message:

This commit is a follow up to the previous work that recorded Libclang invocations
into temporary files: r319702.

It adds a new -cc1 mode to clang: -cc1gen-reproducer. The goal of this mode is to generate
Clang reproducer files for Libclang tool invocation. The JSON format in the invocation
files is not really intended to be stable, so Libclang and Clang should be of the same version
when generating reproducers.
The new mode emits the information about the temporary files and Libclang-specific information
to stdout using JSON.

rdar://35322614

Differential Revision: https://reviews.llvm.org/D40983

llvm-svn: 329465