atmega_common: refactor avr-libc-extra into avr_libc_extra module

boards/common/atmega/board.c

@@ -31,8 +31,13 @@ void led_init(void);
 
 void board_init(void)
 {
+
     atmega_set_prescaler(CPU_ATMEGA_CLK_SCALE_INIT);
+
+#ifdef MODULE_AVR_LIBC_EXTRA
     atmega_stdio_init();
+#endif
+
     cpu_init();
     led_init();
     irq_enable();

boards/waspmote-pro/board.c

@@ -58,7 +58,10 @@ void board_init(void)
 #endif
 #endif
 
+#ifdef MODULE_AVR_LIBC_EXTRA
     atmega_stdio_init();
+#endif
+
     cpu_init();
     led_init();
     irq_enable();

cpu/atmega_common/Makefile

@@ -2,6 +2,6 @@
 MODULE = atmega_common
 
 # add a list of subdirectories, that should also be build
-DIRS = periph
+DIRS = periph avr_libc_extra
 
 include $(RIOTBASE)/Makefile.base

cpu/atmega_common/Makefile.include

@@ -18,7 +18,9 @@ export USEMODULE += periph_common
 export USEMODULE += stdio_uart
 
 # include module specific includes
-export INCLUDES += -I$(RIOTCPU)/atmega_common/include -isystem$(RIOTCPU)/atmega_common/include/vendor
+export INCLUDES += -I$(RIOTCPU)/atmega_common/include \
+                   -isystem$(RIOTCPU)/atmega_common/avr_libc_extra/include \
+                   -isystem$(RIOTCPU)/atmega_common/avr_libc_extra/include/vendor
 
 ifeq ($(LTO),1)
   # avr-gcc <4.8.3 has a bug when using LTO which causes a warning to be printed always:
@@ -37,3 +39,6 @@ LINKFLAGS += $(LINKFLAGPREFIX)--defsym=__DATA_REGION_LENGTH__=$(RAM_LEN)
 LDSCRIPT_COMPAT = $(if $(shell $(TARGET_ARCH)-ld --verbose | grep __TEXT_REGION_LENGTH__),,\
                     -T$(RIOTCPU)/$(CPU)/ldscripts_compat/avr_2.26.ld)
 LINKFLAGS += $(LDSCRIPT_COMPAT)
+
+# avr libc needs some RIOT-specific support code
+USEMODULE += avr_libc_extra

cpu/atmega_common/avr_libc_extra/Makefile

@@ -0,0 +1 @@
+include $(RIOTBASE)/Makefile.base