Log message:
Update libgcroots to 0.2.2.

* Build fix for Mac OS X.
* Enable automake-1.11.

Log message:
Simply and speed up buildlink3.mk files and processing.
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.

Log message:
Import libgcroots version 0.2.1.

This library abstracts architecture-dependent part of garbage collector
roots acquisition such as register windows of SPARC and register stack
backing store of IA-64. Main part of the code is based on Boehm GC 7.0.

With this library, you can easily write your own garbage collector such as
for small footprint, some application-specific optimizations, just learning
or to test experimental ideas.