POSIX does not support grouping in case item patterns.
Installing with a strict POSIX shell fails with:
/usr/local/plan9/bin/9c: line 82: syntax error near unexpected token `('
/usr/local/plan9/bin/9c: line 82: `*(DragonFly|BSD)*gcc*) usegcc ;;'
This change expands the patterns to work around the limitation.
See https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_10
(and search for case_clause)