Buildscript: fix cleanning environment

In the buildscript we are "cleaning the environment" by doing the following:

cleanEnvironment()
{
    export AS=""
    export CCAS=""
    export ASCPP=""
    export CC=""
    export CFLAGS=""
    export CPPFLAGS=""
    export CXX=""
    export CXXFLAGS=""
    export CXXCPPFLAGS=""
    export OBJC=""
    export OBJCFLAGS=""
    export LD=""
    export LDFLAGS=""
    export STRIP=""
    export PKG_CONFIG_LIBDIR=""
    export PKG_CONFIG_PATH=""
}

We should review either we need to clean some variable since we aren't exporting them later on with some correct values in the script.