intercal-0.31 fails to build with -fno-common or gcc-10

Forwarding Gentoo bug 711902.

/usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: parser.o:(.bss+0x14): multiple definition of `yydebug'; src/perpet.o:(.bss+0x88): first defined here
collect2: error: ld returned 1 exit status

gcc-10 and above flipped a default from -fcommon to -fno-common: https://gcc.gnu.org/PR85678

More details are at https://wiki.gentoo.org/wiki/Gcc_10_porting_notes/fno_common

Patch that fixes the problem for me: https://gitweb.gentoo.org/repo/gentoo.git/tree/dev-lang/c-intercal/files/c-intercal-31.0-no-common.patch