rewrite option descriptors to be single string

This reduces the number of relocations on PIE binaries, and also
reduces the executable size. Parsing of the options is slightly
sped up as only the exact matching option group parser is called.
2 jobs for generate-help in 41 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #109466
docker-alpine x86_64
test:alpine

00:00:38

passed #109467
docker-alpine x86_64
test:debian

00:00:39