[Clang] Add a new clang option "-ftime-trace=<value>"

The time profiler traces the stages during the clang compile
process. Each compiling stage of a single source file
corresponds to a separately .json file which holds its
time tracing data. However, the .json files are stored in the
same path/directory as its corresponding stage's '-o' option.
For example, if we compile the "demo.cc" to "demo.o" with option
"-o /tmp/demo.o", the time trace data file path is "/tmp/demo.json".

A typical c++ project can contain multiple source files in different
path, but all the json files' paths can be a mess.

The option "-ftime-trace=<value>" allows you to specify where the json
files should be stored. This allows the users to place the time trace
data files of interest in the desired location for further data analysis.

Usage:
    - clang/clang++ -ftime-trace ...
    - clang/clang++ -ftime-trace=the-directory-you-want ...
    - clang/clang++ -ftime-trace=the-directory-you-want/ ...
    - clang/clang++ -ftime-trace=the-full-file-path-you-want ...

Differential Revision: https://reviews.llvm.org/D128048