fixed: fixed Serial.printf(%f) not working

Author: LynnL4

platform.txt

@@ -47,7 +47,7 @@ compiler.objcopy.eep.flags=-O ihex -j .eeprom --set-section-flags=.eeprom=alloc,
 compiler.elf2hex.bin.flags=-O binary
 compiler.elf2hex.hex.flags=-O ihex -R .eeprom
 compiler.elf2hex.cmd=arm-none-eabi-objcopy
-compiler.ldflags=-mcpu={build.mcu} -mthumb -Wl,--cref -Wl,--check-sections -Wl,--gc-sections -Wl,--unresolved-symbols=report-all -Wl,--warn-common -Wl,--warn-section-align
+compiler.ldflags=-mcpu={build.mcu} -mthumb -Wl,--cref -Wl,--check-sections -Wl,--gc-sections -Wl,--unresolved-symbols=report-all -Wl,--warn-common -Wl,--warn-section-align -u _printf_float -u _scanf_float
 compiler.size.cmd=arm-none-eabi-size
 compiler.define=-DARDUINO=
 compiler.readelf.cmd=arm-none-eabi-readelf
@@ -71,7 +71,7 @@ compiler.ar.extra_flags=
 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.arm.cmsis.ldflags="-L{runtime.tools.CMSIS-4.5.0.path}/CMSIS/Lib/GCC/" -larm_cortexM0l_math 
 
 compiler.libraries.ldflags=