So, it does appear that /usr/src/gcc-10/gcc-10.2.0-dfsg.tar.xz from gcc-10-source 10.2.1-6 , doesn't have these patches applied. And the patches need to be applied manually after unpacking.
/usr/src/gcc-10/debian/README.source provides some information, but it is a bit tricky: user@debian:~/xtensa-d/gcc-xtensa-lx106-8$ /usr/src/gcc-10/debian/rules patch /usr/src/gcc-10/debian/rules:21: debian/rules.patch: No such file or directory make: *** No rule to make target 'debian/rules.patch'. Stop. user@debian:~/xtensa-d/gcc-xtensa-lx106-8 Try to call make -f without changing directory: user@debian:~/xtensa-d/gcc-xtensa-lx106-8$ make -f /usr/src/gcc-10/debian/rules.patch patch make: Nothing to be done for 'patch'. user@debian:~/xtensa-d/gcc-xtensa-lx106-8$ But, I think this is simply because then debian/rules.patch runs without proper variables from rules.defs applied, and $(patch_stamp) is empty string. Not sure how to do all the patches, not that xtensa really need most of them. Just the gdc-texinfo.patch