cc/gcc: set CXXFLAGS at configure gcc

Since gcc 4.8 C++ is also used as implementation language (see gcc
release notes).

Signed-off-by: "Daniel Dittmann" <ddittmann@gmx.net>
Message-Id: <acc7d11bc77b30f21c5b.1388863298@bernalk.machteam>
Patchwork-Id: 306883

 python

 import sys

 sys.path.insert(0, '@@PREFIX@@/share/gcc-@@VERSION@@/python')

 from libstdcxx.v6.printers import register_libstdcxx_printers

 register_libstdcxx_printers (None)

 end