Use -fstandalone-debug for few tests to get around a Clang optimization

clang-3.5+ outputs FullDebugInfo by default for Darwin/FreeBSD targets.
Other targets do not, which causes several tests to fail.  This flag
enables FullDebugInfo for all targets.

Fixes the following tests:

TestCallStdStringFunction.py
TestDataFormatterSkipSummary.py
TestDataFormatterStdIterator.py
TestDataFormatterStdList.py
TestDataFormatterStdString.py
TestSBValuePersist.py
TestStringPrinter.py
TestTypeCompletion.py

llvm-svn: 230831