Cleanup packing lists for xtoolchain gcc packages.

[jhb]

Summary

• Add missing entries for gcov-dump and the gcov-tool manpage to the various xtoolchain gcc ports.
• Add gcov-dump to the post-install loops that handle optional renaming of tools and manpages.

Test Plan

• poudriere testport of aarch64-gcc, amd64-gcc, i386-gcc, mips-gcc, mips64-gcc, powerpc64-gcc, riscv64-gcc (already fine), and sparc64-gcc