[Windows] XFAIL tests that depend on expression name lookup.

Name lookup doesn't work properly with Windows targets.  This is
most likely due to issues with name mangling, although there is at
least one set of debug info related issues as well, since some of
the name lookup requests appear to be failing on types rather than
symbols.

Specifically, this patch XFAILS the following set of tests:

TestChar1632T.py
TestRdar12991846.py
TestConstVariables.py
TestCallCPPFunction.py
TestCallStopAndContinue.py
TestCallUserDefinedFunction.py
TestCModules.py
TestCPPThis.py
TestExprs2.py
TestOverloadedFunctions.py
TestRvalueReferences.py

And fixing the underlying issue is tracked in http://llvm.org/pr24489

llvm-svn: 245338