Define AM_RECURSIVE_TARGETS, for gnulib's GNUmakefile. This new macro lists all public targets which invoke `make' recursively, or depend on targets which do so. It allows to prevent parallelism selectively, when multiple targets are passed on the `make' command line. * lib/am/distdir.am [%?SUBDIRS%] (AM_RECURSIVE_TARGETS): New macro. * lib/am/subdirs.am (AM_RECURSIVE_TARGETS): Likewise. * lib/am/tags.am [%?SUBDIRS%] (AM_RECURSIVE_TARGETS): Likewise. Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>