Allow precompiled libraries on samd core

Author: facchinm

platform.txt

@@ -67,6 +67,8 @@ compiler.elf2hex.extra_flags=
 compiler.arm.cmsis.c.flags="-I{runtime.tools.CMSIS-4.5.0.path}/CMSIS/Include/" "-I{runtime.tools.CMSIS-Atmel-1.2.0.path}/CMSIS/Device/ATMEL/"
 compiler.arm.cmsis.ldflags="-L{runtime.tools.CMSIS-4.5.0.path}/CMSIS/Lib/GCC/" -larm_cortexM0l_math
 
+compiler.libraries.ldflags=
+
 # USB Flags
 # ---------
 build.usb_flags=-DUSB_VID={build.vid} -DUSB_PID={build.pid} -DUSBCON '-DUSB_MANUFACTURER={build.usb_manufacturer}' '-DUSB_PRODUCT={build.usb_product}'
@@ -93,7 +95,7 @@ archive_file_path={build.path}/{archive_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}"  "-L{build.path}" {compiler.c.elf.flags} {compiler.c.elf.extra_flags} "-T{build.variant.path}/{build.ldscript}" "-Wl,-Map,{build.path}/{build.project_name}.map" --specs=nano.specs --specs=nosys.specs {compiler.ldflags} -o "{build.path}/{build.project_name}.elf" {object_files} -Wl,--start-group {compiler.arm.cmsis.ldflags} -lm "{build.path}/{archive_file}" -Wl,--end-group
+recipe.c.combine.pattern="{compiler.path}{compiler.c.elf.cmd}"  "-L{build.path}" {compiler.c.elf.flags} {compiler.c.elf.extra_flags} "-T{build.variant.path}/{build.ldscript}" "-Wl,-Map,{build.path}/{build.project_name}.map" --specs=nano.specs --specs=nosys.specs {compiler.ldflags} -o "{build.path}/{build.project_name}.elf" {object_files} {compiler.libraries.ldflags} -Wl,--start-group {compiler.arm.cmsis.ldflags} -lm "{build.path}/{archive_file}" -Wl,--end-group
 
 ## Create output (bin file)
 recipe.objcopy.bin.pattern="{compiler.path}{compiler.elf2hex.cmd}" {compiler.elf2hex.bin.flags} {compiler.elf2hex.extra_flags} "{build.path}/{build.project_name}.elf" "{build.path}/{build.project_name}.bin"