Add support for report execution times

-Added command line option -report-times to enable or disable the output. The
same option can be used to specify the output directory.
-Write timing data to a unique file in disk using json format.


git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@183142 91177308-0d34-0410-b5e6-96231b3b80d8