Interesting items from ChangeLog:
o cached_realpath(): avoid hitting filesystem more than necessary.
o meta.c: refactor need_meta decision, add knobs for
missing meta file and filemon data wrt out-of-datedness.
o meta.c: missing filemon data is only relevant if we read a
meta file.
Also do not return oodate for a missing metafile if gn->path
points to .CURDIR
Interesting changes (from ChangeLog):
o meta.c: ignore paths that match .MAKE.META.IGNORE_PATTERNS
this is useful for gcov builds.
o propagate errors from filemon(4).
o meta.c: apply realpath() before matching against metaIgnorePaths
o allow makefile to set .MAKE.JOBS