Fix recipe.ar.pattern to avoid warning at startup

Author: facchinm

platform.txt

@@ -63,7 +63,7 @@ recipe.c.o.pattern="{compiler.path}{compiler.c.cmd}" {compiler.c.flags} -DF_CPU=
 recipe.cpp.o.pattern="{compiler.path}{compiler.cpp.cmd}" {compiler.cpp.flags} -DF_CPU={build.f_cpu} -DARDUINO={runtime.ide.version} -DARDUINO_{build.board} -DARDUINO_ARCH_{build.arch} {compiler.cpp.extra_flags} {build.extra_flags} {includes} "{source_file}" -o "{object_file}"
 
 ## Create archives
-recipe.ar.pattern="{compiler.path}{compiler.ar.cmd}" {compiler.ar.flags} {compiler.ar.extra_flags} "{build.path}/{archive_file}" "{object_file}"
+recipe.ar.pattern="{compiler.path}{compiler.ar.cmd}" {compiler.ar.flags} {compiler.ar.extra_flags} "{archive_file_path}" "{object_file}"
 
 ## Combine gc-sections, archives, and objects
 recipe.c.combine.pattern="{compiler.path}{compiler.c.elf.cmd}" {compiler.c.elf.flags} "-T{build.variant.path}/{build.ldscript}" "-Wl,-Map,{build.path}/{build.project_name}.map" {compiler.c.elf.extra_flags} -o "{build.path}/{build.project_name}.elf" "-L{build.path}" "-L{build.variant.path}" -Wl,--whole-archive "-l{build.variant_system_lib}" -Wl,--no-whole-archive -Wl,--start-group "-l{build.variant_system_lib}" -lc -lm -lgcc {object_files} "{build.path}/{archive_file}"