Assorted test suite fixes as a result of GCC 4.8 validation efforts

- disable some TestConcurrentEvents cases (which are affected by llvm.org/pr16714 -- watchpoints in multithreaded programs)
- relax number-of-bp-locations check in TestUniqueTypes/TestUnsignedTypes
- skip TestDataFormatterStdVector cases with GCC 4.8 (known failure due to llvm.org/pr15301)
- workaround for race condition in TestHelloWorld.py
- update TestSettings.py to work on distros (like Fedora) that have /bin/cat hardlinked to /usr/bin/cat

After these changes, the test suite should run cleanly against GCC 4.8 (with DWARF v4)!

llvm-svn: 187451