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.