add picoboot-lib support

Author: nerdralph

avr/platform.txt

@@ -39,7 +39,8 @@ compiler.objcopy.cmd=avr-objcopy
 compiler.objcopy.eep.flags=-O ihex -j .eeprom --set-section-flags=.eeprom=alloc,load --no-change-warnings --change-section-lma .eeprom=0
 compiler.elf2hex.flags=-O ihex -R .eeprom
 compiler.elf2hex.cmd=avr-objcopy
-#compiler.ldflags=
+compiler.ldflags=-Wl,--section-start=.bootloader=0x1f00
+compiler.libraries.ldflags=
 compiler.size.cmd=avr-size
 
 # This can be overridden in boards.txt
@@ -74,7 +75,7 @@ recipe.ar.pattern="{compiler.path}{compiler.ar.cmd}" {compiler.ar.flags} {compil
 
 ## Combine gc-sections, archives, and objects
 #recipe.c.combine.pattern="{compiler.path}{compiler.c.elf.cmd}" {compiler.c.elf.flags} -mmcu={build.mcu} {compiler.c.elf.extra_flags} -o "{build.path}/{build.project_name}.elf" {object_files} "{build.path}/{archive_file}" "-L{build.path}" -lm
-recipe.c.combine.pattern="{compiler.path}{compiler.c.elf.cmd}" {compiler.c.elf.flags} -mmcu={build.mcu} {compiler.c.elf.extra_flags} -o "{build.path}/{build.project_name}.elf" {object_files} "{build.path}/{archive_file}" "-L{build.path}" -lm
+recipe.c.combine.pattern="{compiler.path}{compiler.c.elf.cmd}" {compiler.c.elf.flags} -mmcu={build.mcu} {compiler.c.elf.extra_flags} {compiler.ldflags} -o "{build.path}/{build.project_name}.elf" {object_files} {compiler.libraries.ldflags} "{build.path}/{archive_file}" "-L{build.path}" -lm
 
 ## Create output files (.eep and .hex)
 recipe.objcopy.eep.pattern="{compiler.path}{compiler.objcopy.cmd}" {compiler.objcopy.eep.flags} {compiler.objcopy.eep.extra_flags} "{build.path}/{build.project_name}.elf" "{build.path}/{build.project_name}.eep"