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.
TECkit is a low-level toolkit intended to be used by other
applications that need to perform encoding conversions (e.g., when
importing legacy data into a Unicode-based application). The primary
component of the TECkit package is therefore a library that performs
conversions; this is the "TECkit engine". The engine relies on
mapping tables in a specific binary format (for which documentation is
available); there is a compiler that creates such tables from a
human-readable mapping description (a simple text file).
