Merge pull request #10854 from cladmi/pr/atmega_common/unexport/linkflags

cpu/atmega_common: do not export LINKFLAGS

cpu/atmega_common/Makefile.include

@@ -8,7 +8,7 @@ export CFLAGS_OPT  ?= -Os
 
 export CFLAGS += $(CFLAGS_CPU) $(CFLAGS_LINK) $(CFLAGS_DBG) $(CFLAGS_OPT)
 export ASFLAGS += $(CFLAGS_CPU) $(CFLAGS_DBG)
-export LINKFLAGS += $(CFLAGS_CPU) $(CFLAGS_DBG) $(CFLAGS_OPT) -static -lgcc -e reset_handler -Wl,--gc-sections
+LINKFLAGS += $(CFLAGS_CPU) $(CFLAGS_DBG) $(CFLAGS_OPT) -static -lgcc -e reset_handler -Wl,--gc-sections
 
 # export the peripheral drivers to be linked into the final binary
 export USEMODULE += atmega_common_periph
@@ -26,7 +26,7 @@ ifeq ($(LTO),1)
   # avr-gcc <4.8.3 has a bug when using LTO which causes a warning to be printed always:
   # '_vector_25' appears to be a misspelled signal handler [enabled by default]
   # See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59396
-  export LINKFLAGS += -Wno-error
+  LINKFLAGS += -Wno-error
 endif
 
 # Use ROM_LEN and RAM_LEN during link