commit 895736d49bd2bb318c69de99a05ea70c035c2da9 made these changes
along with fixing a real bug in LOG_MAKEPRI. based on further
information, they do not seem to be well-motivated or in line with
policy.
the result of LOG_FAC is not a meaningful facility value if we shift
it down like before, but apparently the way it is used by applications
is as an index into an array of facility names. moreover, all
historical systems which define it do so with the shift. as it is a
nonstandard interface, there is no justification for providing a macro
by the same name that is incompatible with historical practice.
the value of LOG_FACMASK likewise is 0x3f8 on all historical systems
checked. while only 5 bits are used for existing facility codes, the
convention seems to be that all 7 bits belong to the facility field
and theoretically could be used to expand to having more facilities.
that seems unlikely to happen, but there is no reason to make a
gratuitously incompatible change here.

these are nonstandard and unnecessary for using the associated
functionality, but resulted in applications that used them
malfunctioning.
patch based on proposed fix by erny hombre.

this issue affected the prioritynames and facilitynames arrays which
are only provided when requested (usually by syslogd implementations)
and which are presently defined as compound literals. the aliasing
violation seems to have been introduced as a workaround for bad
behavior by gcc's -Wwrite-strings option, but it caused compilers to
completely optimize out the contents of prioritynames and
facilitynames since, under many usage cases, the aliasing rules prove
that the contents are never accessed.

another commit to silence gcc warnings (-Wparentheses) for standard headers.
changed macros: LOG_UPTO, IN6_ARE_ADDR_EQUAL

some macros in sys/mtio.h and syslog.h used NULL without defining it

the old behavior of exposing nothing except plain ISO C can be
obtained by defining __STRICT_ANSI__ or using a compiler option (such
as -std=c99) that predefines it. the new default featureset is POSIX
with XSI plus _BSD_SOURCE. any explicit feature test macros will
inhibit the default.
installation docs have also been updated to reflect this change.

one file was reusing another file's macro name, and many had
inconsistent underscores and application of SYS prefix, etc.
patch by Szabolcs Nagy (nsz)

patch by Isaac Dunham. matched closely (maybe not exact) to glibc's
idea of what _BSD_SOURCE should make visible.