Add carefully crafted Makefile for recursing into subdirectories...

that is compatile with both real Make and GNU Make.

mk/bld.mk

@@ -0,0 +1,28 @@
+# Makefile to build in the subdirectories.
+# Designed to be both BSD Make and GNU Make compatible
+# (as are all the other Makefiles).
+#
+
+# The RECURSE macro uses a shell variable $TARGET for delayed expansion.
+RECURSE=for d in bld-* ; \
+	do \
+	    ${MAKE} -C $$d $${TARGET} ; \
+	done
+
+# This carefully crafted rule will run Make in all subdirectories with
+# the same target, no matter what it is (as long as it is just one
+# target).
+#
+# .TARGETS is a BSD specific variable, and MAKECMDGOALS is the GNU version.
+# .TARGETS becomes "rEmOvEmE" when no targets are given on the
+# command line (because this is the default target).
+# MAKECMDGOALS remains empty in that case.
+# Do not use "all" as the extra target, since that fails when that is
+# given as target on the command line (you get duplicate targets).
+# The shell variable substitution removes "rEmOvEmE" if present.
+# So when no target is given, the recursion uses no target either.
+
+${.TARGETS} ${MAKECMDGOALS} rEmOvEmE :
+#	set -x; T="${.TARGETS}${MAKECMDGOALS}"; echo "T=$$T"; TARGET="$${T%%rEmOvEmE}"; echo "TARGET=$$TARGET"
+	T="${.TARGETS}${MAKECMDGOALS}"; TARGET="$${T%%rEmOvEmE}"; ${RECURSE}
+