[gentoo-dev] RFC: make system-sqlite a global USE flag

$ euse --info system-sqlite
global use flags (searching: system-sqlite)
************************************************************
no matching entries found

local use flags (searching: system-sqlite)
************************************************************
[-    ] system-sqlite (mail-client/thunderbird):
Use the system-wide dev-db/sqlite installation with secure-delete enabled

[-    ] system-sqlite (net-libs/xulrunner):
Use the system-wide dev-db/sqlite installation with secure-delete enabled

[-    ] system-sqlite (www-client/chromium):
Use the system-wide dev-db/sqlite installation with secure-delete enabled

[-    ] system-sqlite (www-client/firefox):
Use the system-wide dev-db/sqlite installation with secure-delete enabled

[-    ] system-sqlite (www-client/icecat):
Use the system-wide dev-db/sqlite installation with secure-delete enabled

[-    ] system-sqlite (www-client/seamonkey):
Use the system-wide dev-db/sqlite installation with secure-delete enabled

[-    ] system-sqlite (x11-plugins/enigmail):
Use the system-wide dev-db/sqlite installation with secure-delete enabled

The meaning is identical in all those cases, and I think the number of
packages may have hit the threshold for a global flag.

However, we already have a very similar global USE flag: sqlite, which
makes this a bit more tricky. The difference is very subtle:

IUSE="sqlite" means "the sqlite support is optional; -sqlite means no
sqlite support"

IUSE="system-sqlite" means "we can use the bundled sqlite or the system
one; -system-sqlite means we use the bundled one; both settings result
in sqlite support"

If we'd make system-sqlite a global USE flag, I'd suggest a description
like "Use the system-wide dev-db/sqlite instead of bundled copy of sqlite."

What do you think?