pybind: move linker flags out of "libraries"

pybind: move linker flags out of "libraries"

sometimes, `distutils.sysconfig.get_config_vars('LIBS')` returns flags
not starting with `-l`, and hence we should not allow
`setuptools.extension.Extension` to rebuild the `-l` options from those
flags, otherwise the linker just fails as the `-l-flags_for_linker` will
be passed to the linker.

in this change, those linker flags are passed directly to linker.

Signed-off-by: Kefu Chai <kchai@redhat.com>