Having the C preprocessor macro CONTIKI_TARGET set to $(TARGET) turned out to be not that useful for conditionals. Therefore I switched to having the macro CONTIKI_TARGET_$(TARGET) set (to the default value of 1).

In order to allow for clean C code with the usual all-uppercase macro names $(TARGET) had to be converted to uppercase. Gnumake doesn't have a builtin string function for doing so, therefore sed is called. The Gnumake doc section 14.2 lists sed as one of the utilities a makefile can always presume to be available. However it states that only generally supported utility options should be used. So the GNU sed extension \U was intentionally avoided.

Makefile.include

@@ -2,9 +2,6 @@ ifndef CONTIKI
   ${error CONTIKI not defined! You must specify where CONTIKI resides}
 endif
 
-OBJECTDIR = obj_$(TARGET)
-CFLAGS += -DCONTIKI_TARGET=$(TARGET)
-
 ifeq ($(TARGET),)
   -include Makefile.target
   ifeq ($(TARGET),)
@@ -38,10 +35,16 @@ savedefines:
 	@echo "saving Makefile.$(TARGET).defines"
 	@echo >Makefile.$(TARGET).defines "DEFINES = $(DEFINES)"
 
+OBJECTDIR = obj_$(TARGET)
 ifeq (${wildcard $(OBJECTDIR)},)
 DUMMY := ${shell mkdir $(OBJECTDIR)}
 endif
 
+LOWERCASE = abcdefghijklmnopqrstuvwxyz
+UPPERCASE = ABCDEFGHIJKLMNOPQRSTUVWXYZ
+TARGET_UPPERCASE := ${shell echo $(TARGET) | sed 'y!$(LOWERCASE)!$(UPPERCASE)!'}
+CFLAGS += -DCONTIKI_TARGET_$(TARGET_UPPERCASE)
+
 include $(CONTIKI)/core/net/rime/Makefile.rime
 include $(CONTIKI)/core/net/mac/Makefile.mac
 SYSTEM  = process.c procinit.c autostart.c elfloader.c profile.c timetable.c timetable-aggregate.c