run_tests.py had bitrotted since it was last run (e.g. it used perl
which is now not allowed and the warning flags were out of date).
I changed it to use a different way of extracting the compile command
which is based on Soong instead of makefiles. This way is also
compatible with multiple build directories since it doesn't clobber
the source directory and doesn't require OUT_DIR == out.
This also changes run_tests.py to run the libcxxabi tests as well,
since they can be run using the same mechanism.
Bug: 120510768
Test: ./run_tests.py --bitness 32
Test: ./run_tests.py --bitness 64
Test: ./run_tests.py --bitness 64 --host
Change-Id: Id30129161f8519fa6c1bc106727326373ca9ab82
