How about promoting syslog to global USE flag?
In addition to the list below, I would need it in mail-filter/dspam.

global use flags (searching: syslog)
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no matching entries found

local use flags (searching: syslog)
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[-    ] syslog (dev-libs/openobex):
enable syslog support

[-    ] syslog (mail-mta/exim):
defines syslog as the default log path if none is specified in the conf
file.

[-    ] syslog (net-firewall/nufw):
Add support user activity logging in syslog

[-    ] syslog (net-fs/samba):
Enables support for syslog

[-    ] syslog (net-misc/partysip):
Enable syslog support