This consolidates all queries to the wrapdb to go through the open_wrapdburl()
function. The function handles a domain-specific url scheme
wrapdb. When encountered, it substitutes the scheme with https and
an authority(netloc) with either upstream wrapdb address or
a user-defined one from the MESON_WRAPDB_MIRROR environment variable.

Environment variables are prone to shell injection attacks, especially
on build servers that many people may have access to. Changing address in
a file requires an explicit command that is supposedly under the control
of a trusted developer.