New toolchain breaks <iostream>

[sylque]

After upgrading from [email protected] to [email protected], the following code doesn't work anymore:

#include <Arduino.h>
#include <iostream>

void setup() {}

void loop() {}

Linking .pio\build\debug\firmware.elf
c:/users/xxx/.platformio/packages/[email protected]/bin/../lib/gcc/arm-none-eabi/8.2.1/../../../../arm-none-eabi/bin/ld.exe: c:/users/xxx/.platformio/packages/[email protected]/bin/../lib/gcc/arm-none-eabi/8.2.1/../../../../arm-none-eabi/lib\libstdc++_nano.a(locale_init.o): in function `(anonymous namespace)::get_locale_mutex()':
(.text._ZN12_GLOBAL__N_116get_locale_mutexEv+0xc): undefined reference to `__sync_synchronize'
c:/users/xxx/.platformio/packages/[email protected]/bin/../lib/gcc/arm-none-eabi/8.2.1/../../../../arm-none-eabi/bin/ld.exe: c:/users/xxx/.platformio/packages/[email protected]/bin/../lib/gcc/arm-none-eabi/8.2.1/../../../../arm-none-eabi/lib\libstdc++_nano.a(locale.o): in function `std::locale::_Impl::_M_install_cache(std::locale::facet const*, unsigned int)':
(.text._ZNSt6locale5_Impl16_M_install_cacheEPKNS_5facetEj+0x18): undefined reference to `__sync_synchronize'
collect2.exe: error: ld returned 1 exit status
*** [.pio\build\debug\firmware.elf] Error 1

(issue initially reported here)

[valeros]

Thanks for reporting, the toolchain package has been downgraded to GCC v7.