Use dev-libs/xxhash to speed up internal hashing

Packages describing “xxhash” as local USE flag

Package “xxhash” Flag Description
media-libs/libplacebo Use dev-libs/xxhash to speed up internal hashing
media-libs/dav1d Enable dev-libs/xxhash support for hashing muxer
sys-devel/gdb Use dev-libs/xxhash to speed up internal hashing.
net-misc/rsync Enable dev-libs/xxhash support for hashing
app-admin/rsyslog Enable xxHash support in fmhash module (requires dev-libs/xxhash)

All packages providing a “xxhash” USE flag (4)