Added support for breakpoint conditions. I also had to separate the "run the...

Added support for breakpoint conditions.  I also had to separate the "run the expression" part of ClangFunction::Execute from the "Gather the expression result" so that in the case of the Breakpoint condition I can move the condition evaluation into the normal thread plan processing.

Also added support for remembering the "last set breakpoint" so that "break modify" will act on the last set breakpoint.

llvm-svn: 116542