+PROJECT_DIRECTORIES := $(shell ls -d */)
+
+# This makefile is potentially infinitely recursive if something really bad
+# happens when determining the set of project directories - hard-abort if
+# more than 10 levels deep to avoid angry emails.
+ifeq ($(MAKELEVEL), 10)
+ $(error EMERGENCY ABORT: INFINITE RECURSION DETECTED)
+endif
+
+# Need to special-case building without a per-project object directory
+ifeq ($(OBJDIR),)
+ # If no target specified, force "clean all" and disallow parallel build
+ ifeq ($(MAKECMDGOALS),)
+ MAKECMDGOALS := clean all
+ .NOTPARALLEL:
+ endif