Update the BUILD build system module to early abort and display an error if...

Update the BUILD build system module to early abort and display an error if needed before trying to create the OBJDIR output object file directory.

LUFA/Build/lufa_build.mk

@@ -152,15 +152,20 @@ endif
 
 # Convert input source filenames into a list of required output object files
 OBJECT_FILES += $(addsuffix .o, $(basename $(SRC)))
+
+# Check if an output object file directory was specified instead of the input file location
 ifneq ($(OBJDIR),.)
-   $(shell mkdir $(OBJDIR) 2> /dev/null)   
-   VPATH           += $(dir $(SRC))
+   # Prefix all the object filenames with the output object file directory path
    OBJECT_FILES    := $(addprefix $(patsubst %/,%,$(OBJDIR))/, $(notdir $(OBJECT_FILES)))
    
    # Check if any object file (without path) appears more than once in the object file list
    ifneq ($(words $(sort $(OBJECT_FILES))), $(words $(OBJECT_FILES)))
        $(error Cannot build with OBJDIR parameter set - one or more object file name is not unique)
    endif
+
+   # Create the output object file directory if it does not exist and add it to the virtual path list
+   $(shell mkdir $(OBJDIR) 2> /dev/null)   
+   VPATH           += $(dir $(SRC))
 endif
 
 # Create a list of dependency files from the list of object files