This changes the buildlink3.mk files to use an include guard for the
recursive include. The use of BUILDLINK_DEPTH, BUILDLINK_DEPENDS,
BUILDLINK_PACKAGES and BUILDLINK_ORDER is handled by a single new
variable BUILDLINK_TREE. Each buildlink3.mk file adds a pair of
enter/exit marker, which can be used to reconstruct the tree and
to determine first level includes. Avoiding := for large variables
(BUILDLINK_ORDER) speeds up parse time as += has linear complexity.
The include guard reduces system time by avoiding reading files over and
over again. For complex packages this reduces both %user and %sys time to
half of the former time.
The System Tools Backends (s-t-b for short) are a set of cross-platform
modules for Linux, FreeBSD and other Unix systems. The backends provide a
common DBus interface to all platforms to modify or read the system
configuration in a distro independent fashion. Historically, access to
system configuration has varied deeply across Unix flavours, and concreting
a bit more, across Linux distributions, making it near impossible to write
desktop tools that could work flawlessly in a cross-platform way. System
Tools Backends try to fill this gap, offering a generic and easy way for
desktop applications to read and modify configuration details.
