py-libxml2: need to either blacklist gcc-4* or patch out -Wno-unused-result

[barracuda156]

gcc-4.2 does not understand this flag, and the build fails.

creating build/temp.macosx-10.6-ppc-cpython-310
/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_python_py-libxml2/py310-libxml2/work/compwrap/cc/usr/bin/gcc-4.2 -Wno-unused-result -Wsign-compare -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -pipe -Os -arch ppc -isysroot/ -D_REENTRANT=1 -I/opt/local/include/libxml2 -I/opt/local/Library/Frameworks/Python.framework/Versions/3.10/include/python3.10 -c libxml.c -o build/temp.macosx-10.6-ppc-cpython-310/libxml.o
cc1: error: unrecognized command line option "-Wno-unused-result"
error: command '/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_python_py-libxml2/py310-libxml2/work/compwrap/cc/usr/bin/gcc-4.2' failed with exit code 1
Command failed:  cd "/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_python_py-libxml2/py310-libxml2/work/libxml2-2.9.14/python" && /opt/local/Library/Frameworks/Python.framework/Versions/3.10/bin/python3.10 setup.py --no-user-cfg build -j4 
Exit code: 1
Error: Failed to build py310-libxml2: command execution failed