How to get fast ~ operator using C locale

["Artur Rataj" <arturrataj@xxxxxxxxx>]

Hello, I want to have pg use fast indexing for ~ operator. Is setting
C locale for this is still necessary? If yes, is it enough to
initdb/createdb with C locale? If it is not enough, why setting locale
to C and starting postmaster still gives other locale, for example,
pl_PL, in
postmaster log "initial environ dump"?

Best regards,
Artur