Minor build system sanity check fixes.

LUFA/Build/lufa.dfu.in

@@ -42,8 +42,6 @@ ERROR_IF_NONBOOL = $(if $(filter Y N, $($(strip $(1)))), , $(error Makefile $(st
 
 # Sanity-check values of mandatory user-supplied variables
 $(foreach MANDATORY_VAR, $(LUFA_BUILD_MANDATORY_VARS), $(call ERROR_IF_UNSET, $(MANDATORY_VAR)))
-$(call ERROR_IF_UNSET, MCU)
-$(call ERROR_IF_UNSET, TARGET)
 $(call ERROR_IF_EMPTY, MCU)
 $(call ERROR_IF_EMPTY, TARGET)
 

LUFA/Build/lufa.doxygen.in

@@ -46,7 +46,7 @@ DOXYGEN_OVERRIDE_PARAMS ?= QUIET=YES HTML_STYLESHEET=$(patsubst %/,%,$(LUFA_PATH
 
 # Sanity check user supplied values
 $(foreach MANDATORY_VAR, $(LUFA_BUILD_MANDATORY_VARS), $(call ERROR_IF_UNSET, $(MANDATORY_VAR)))
-$(call ERROR_IF_EMPTY, LUFA_PATH)
+$(call ERROR_IF_EMPTY, DOXYGEN_CONF)
 $(call ERROR_IF_EMPTY, LUFA_PATH)
 $(call ERROR_IF_NONBOOL, DOXYGEN_FAIL_ON_WARNING)