Bug#697755: llvm-3.2: Please, cleanup compilation flags reported by llvm-config

[Morten Hustveit]

The --cppflags and --cxxflags options are also offenders, adding these
flags, which are not really required for programs using llvm, and may
even be unwanted:

  -DNDEBUG
  -O2
  -g
  -fomit-frame-pointer
  -fPIC
  -Woverloaded-virtual
  -Wcast-qual

In particular, I don't want -O2 when I'm trying trying to debug using
gdb.  -DNDEBUG disables all my asserts.