Enable floating point formatting in sprintf/sscanf (#1179)

Author: igrr

platform.txt

@@ -31,7 +31,7 @@ compiler.c.flags=-c {compiler.warning_flags} -Os -g -Wpointer-arith -Wno-implici
 compiler.S.cmd=xtensa-lx106-elf-gcc
 compiler.S.flags=-c -g -x assembler-with-cpp -MMD -mlongcalls
 
-compiler.c.elf.flags=-g {compiler.warning_flags} -Os -nostdlib -Wl,--no-check-sections -u call_user_start -Wl,-static "-L{compiler.sdk.path}/lib" "-L{compiler.sdk.path}/ld" "-L{compiler.libc.path}/lib" "-T{build.flash_ld}" -Wl,--gc-sections -Wl,-wrap,system_restart_local -Wl,-wrap,register_chipv6_phy
+compiler.c.elf.flags=-g {compiler.warning_flags} -Os -nostdlib -Wl,--no-check-sections -u call_user_start -u _printf_float -u _scanf_float -Wl,-static "-L{compiler.sdk.path}/lib" "-L{compiler.sdk.path}/ld" "-L{compiler.libc.path}/lib" "-T{build.flash_ld}" -Wl,--gc-sections -Wl,-wrap,system_restart_local -Wl,-wrap,register_chipv6_phy
 
 compiler.c.elf.cmd=xtensa-lx106-elf-gcc
 compiler.c.elf.libs=-lhal -lphy -lpp -lnet80211 {build.lwip_lib} -lwpa -lcrypto -lmain -lwps -laxtls -lsmartconfig -lmesh -lwpa2 -lstdc++ -lm -lc -lgcc