Add support for sys-libs/gdbm (GNU database libraries)

Packages describing “gdbm” as local USE flag

Package“gdbm” Flag Description
mail-client/muttEnable sys-libs/gdbm database backend for header caching
mail-client/neomuttEnable GDBM (GNU dbm) backend for header caching
mail-filter/pyzorEnables the Gdbm back-end database engine for pyzord
media-sound/pulseaudio-daemonUse sys-libs/gdbm to store PulseAudio databases. Recommended for desktop usage. This flag causes the whole package to be licensed under GPL-2 or later.
net-firewall/fwknopUse sys-libs/gdbm to store fwknopd digest cache

All packages providing a “gdbm” USE flag (26)