Reduce makefile code duplication

arch/cpu/arm/cortex-m/Makefile.cortex-m

@@ -3,6 +3,18 @@ CONTIKI_ARM_DIRS += cortex-m cortex-m/CMSIS
 ### Build syscalls for newlib
 MODULES += os/lib/newlib
 
+LDFLAGS += -T $(LDSCRIPT)
+LDFLAGS += -Wl,--gc-sections,--sort-section=alignment
+LDFLAGS += -Wl,-Map=$(CONTIKI_NG_PROJECT_MAP),--cref,--no-warn-mismatch
+
+OBJCOPY_FLAGS += --gap-fill 0xff
+
+CPU_STARTFILES = ${addprefix $(OBJECTDIR)/,${call oname, $(CPU_START_SOURCEFILES)}}
+
+### Resolve any potential circular dependencies between the linked libraries
+### See: https://stackoverflow.com/questions/5651869/gcc-what-are-the-start-group-and-end-group-command-line-options/5651895
+TARGET_LIBFLAGS := -Wl,--start-group $(TARGET_LIBFILES) -Wl,--end-group
+
 CUSTOM_RULE_LINK = 1
 
 .SECONDEXPANSION:

arch/cpu/arm/cortex-m/cm3/Makefile.cm3

@@ -3,16 +3,7 @@ CONTIKI_ARM_DIRS += cortex-m/cm3
 CFLAGS += -mcpu=cortex-m3
 
 LDFLAGS += -mcpu=cortex-m3 -nostartfiles
-LDFLAGS += -T $(LDSCRIPT)
-LDFLAGS += -Wl,--gc-sections,--sort-section=alignment
-LDFLAGS += -Wl,-Map=$(CONTIKI_NG_PROJECT_MAP),--cref,--no-warn-mismatch
 
-OBJCOPY_FLAGS += --gap-fill 0xff
-
-CPU_STARTFILES = ${addprefix $(OBJECTDIR)/,${call oname, $(CPU_START_SOURCEFILES)}}
-
-### Resolve any potential circular dependencies between the linked libraries
-### See: https://stackoverflow.com/questions/5651869/gcc-what-are-the-start-group-and-end-group-command-line-options/5651895
-TARGET_LIBFLAGS := -Wl,--start-group $(TARGET_LIBFILES) -lm -Wl,--end-group
+TARGET_LIBFILES += -lm
 
 include $(CONTIKI)/arch/cpu/arm/cortex-m/Makefile.cortex-m

arch/cpu/arm/cortex-m/cm4/Makefile.cm4

@@ -3,16 +3,5 @@ CONTIKI_ARM_DIRS += cortex-m/cm4
 CFLAGS += -mcpu=cortex-m4
 
 LDFLAGS += -mcpu=cortex-m4
-LDFLAGS += -T $(LDSCRIPT)
-LDFLAGS += -Wl,--gc-sections,--sort-section=alignment
-LDFLAGS += -Wl,-Map=$(CONTIKI_NG_PROJECT_MAP),--cref,--no-warn-mismatch
-
-OBJCOPY_FLAGS += --gap-fill 0xff
-
-CPU_STARTFILES = ${addprefix $(OBJECTDIR)/,${call oname, $(CPU_START_SOURCEFILES)}}
-
-### Resolve any potential circular dependencies between the linked libraries
-### See: https://stackoverflow.com/questions/5651869/gcc-what-are-the-start-group-and-end-group-command-line-options/5651895
-TARGET_LIBFLAGS := -Wl,--start-group $(TARGET_LIBFILES) -Wl,--end-group
 
 include $(CONTIKI)/arch/cpu/arm/cortex-m/Makefile.cortex-m