packages/gcc: For targets (libstdc++,java,mudflap...) use xgcc -E as CPP

packages/gcc: For targets (libstdc++,java,mudflap...) use xgcc -E as CPP
    GCC compiles the xgcc cross compiler and will compile target
    libraries e.g. libstdc++. It uses autoconf to configure the target
    libraries which uses /usr/bin/cpp to determine the presence of
    host includes.
    By using xgcc we will not risk to include /usr/include to find standard
    headers. If we do our cross compile check will hit.
    The gcc 3.4 series patch only addresses target-libstdc++ where the
    gcc3.3 and gcc4 series patch all targets