package/python3: fix configure issue for musl/uclibc GCC 8+ toolchains on powerpc

package/python3: fix configure issue for musl/uclibc GCC 8+ toolchains on powerpc

Fixes:
http://autobuild.buildroot.net/results/cb4/cb49c539501342e45cbe5ade82e588fcdf51f05b

GCC commit 6834b83784dcf0364eb820e8 (multiarch support for non-glibc linux
systems), which is part of GCC 8+, changed the multiarch logic to use
$arch-linux-musl / $arch-linux-uclibc rather than $arch-linux-gnu.

This then causes the python3 configure script to error out:

checking for the platform triplet based on compiler characteristics... powerpc-linux-gnu
configure: error: internal configure error for the platform triplet, please file a bug report

http://autobuild.buildroot.net/results/cb4/cb49c539501342e45cbe5ade82e588fcdf51f05b

As it requires that the --print-multiarch output (if not empty) matches the
deduced triplet (which always uses -linux-gnu).

It isn't quite clear why --print-multiarch returns something for a
non-multiarch toolchain on some architectures (E.G.  PowerPC), but as a
workaround, add a patch to rewrite the --print-multiarch output to match
older GCC versions to keep the configure script happy.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>