Adjust parallelism settings again.

Author: davidgiven

build/ab.mk

@@ -113,7 +113,8 @@ $(OBJ)/build.ninja $(OBJ)/build.targets &:
 		|| (rm -f $@ && false)
 
 include $(OBJ)/build.targets
-.NOTPARALLEL: $(ninja-targets)
-.PHONY: $(ninja-targets)
-$(ninja-targets) : $(OBJ)/build.ninja
+.PHONY: $(ninja-targets) invoke-ninja
+.NOTPARALLEL: invoke-ninja
+$(ninja-targets): invoke-ninja
+invoke-ninja: $(OBJ)/build.ninja
 	+$(hide) $(NINJA) -f $(OBJ)/build.ninja $@