Refactor make suffix rules into separate files (one for POSIX and one not),
and rationalise the rules so that bsd.lib.mk can contain only those rules
that are library-specific (.c.po and .c.So).
This can be accomplished by adding ${STATIC_CFLAGS} to the .c.o rule
unconditionally. STATIC_CFLAGS are only defined for use by sys.mk rules in
lib/libpam/Makefile.inc (see r227797), so it should (should?) be safe to
include them unconditionally in sys.mk's .c.o rule.