Well, the move operators were part of C++11 anyway, so I doubt that GNU made the difference. I tried with the build_unflags=
/build_flags=
option you proposed to no avail.
The error I got with the new toolchain are concentrating on one source file in the ESP8266WiFi domain:
In file included from c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.2.0\cstdlib:75,
from c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.2.0\bits\stl_algo.h:59,
from c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.2.0\algorithm:62,
from C:\Users\Micha\.platformio\packages\framework-arduinoespressif8266\libraries\ESP8266WiFi\src\WiFiClientSecureBearSSL.cpp:27:
c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\stdlib.h:94:44: error: expected initializer before '__result_use_check'
94 | void *calloc(size_t, size_t) __malloc_like __result_use_check
| ^~~~~~~~~~~~~~~~~Compiling .pio\build\esp8285\libe3a\ESPAsyncTCP\ESPAsyncTCPbuffer.cpp.o
~
c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\stdlib.h:112:36: error: expected initializer before '__result_use_check'
112 | void *malloc(size_t) __malloc_like __result_use_check __alloc_size(1) _NOTHROW;
| ^~~~~~~~~~~~~~~~~~
Compiling .pio\build\esp8285\libe3a\ESPAsyncTCP\SyncClient.cpp.o
In file included from c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.2.0\cstdlib:75,
from c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.2.0\bits\stl_algo.h:59,
from c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.2.0\algorithm:62,
from C:\Users\Micha\.platformio\packages\framework-arduinoespressif8266\libraries\ESP8266WiFi\src\WiFiClientSecureBearSSL.cpp:27:
c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\stdlib.h:149:31: error: expected initializer before '__result_use_check'
149 | void *realloc(void *, size_t) __result_use_check __alloc_size(2) _NOTHROW;
| ^~~~~~~~~~~~~~~~~~
c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\stdlib.h:151:44: error: expected initializer before '__result_use_check'
151 | void *reallocarray(void *, size_t, size_t) __result_use_check __alloc_size2(2, 3);
| ^~~~~~~~~~~~~~~~~~
c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\stdlib.h:152:32: error: expected initializer before '__result_use_check'
152 | void *reallocf(void *, size_t) __result_use_check __alloc_size(2);
| ^~~~~~~~~~~~~~~~~~
c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\stdlib.h:293:6: error: expected initializer before '__result_use_check'
293 | __result_use_check;
| ^~~~~~~~~~~~~~~~~~
c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\stdlib.h:336:52: error: expected initializer before '__alloc_align'
336 | void * aligned_alloc(size_t, size_t) __malloc_like __alloc_align(1)
| ^~~~~~~~~~~~~
In file included from c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.2.0\bits\stl_algo.h:59,
from c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.2.0\algorithm:62,
from C:\Users\Micha\.platformio\packages\framework-arduinoespressif8266\libraries\ESP8266WiFi\src\WiFiClientSecureBearSSL.cpp:27:
c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.2.0\cstdlib:144:11: error: 'calloc' has not been declared in '::'
144 | using ::calloc;
| ^~~~~~
c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.2.0\cstdlib:151:11: error: 'malloc' has not been declared in '::'
151 | using ::malloc;
| ^~~~~~
c:\users\micha\.platformio\packages\toolchain-xtensa\xtensa-lx106-elf\include\c++\10.2.0\cstdlib:164:11: error: 'realloc' has not been declared in '::'
164 | using ::realloc;
| ^~~~~~~
In file included from C:\Users\Micha\.platformio\packages\framework-arduinoespressif8266\tools\sdk\lwip\include/arch/cc.h:43,
from C:\Users\Micha\.platformio\packages\framework-arduinoespressif8266\tools\sdk\lwip\include/lwip/arch.h:43,
from C:\Users\Micha\.platformio\packages\framework-arduinoespressif8266\tools\sdk\lwip\include/lwip/debug.h:35,
from C:\Users\Micha\.platformio\packages\framework-arduinoespressif8266\tools\sdk\lwip\include/lwip/opt.h:46,
from C:\Users\Micha\.platformio\packages\framework-arduinoespressif8266\tools\sdk\lwip\include/lwip/init.h:35,
from C:\Users\Micha\.platformio\packages\framework-arduinoespressif8266\cores\esp8266/IPAddress.h:27,
from C:\Users\Micha\.platformio\packages\framework-arduinoespressif8266\libraries\ESP8266WiFi\src\ESP8266WiFi.h:31,
from C:\Users\Micha\.platformio\packages\framework-arduinoespressif8266\libraries\ESP8266WiFi\src\WiFiClientSecureBearSSL.cpp:34:
c:\users\micha\.platformio\packages\framework-arduinoespressif8266\cores\esp8266\core_esp8266_features.h: In function 'T* arduino::new0(size_t, TConstructorArgs ...)':
c:\users\micha\.platformio\packages\framework-arduinoespressif8266\cores\esp8266\core_esp8266_features.h:50:22: error: there are no arguments to 'malloc' that depend on a template parameter, so a declaration of 'malloc' must be available [-fpermissive]
50 | T* ptr = (T*)malloc(offset + (arraysize * sizeof(T)));
| ^~~~~~
c:\users\micha\.platformio\packages\framework-arduinoespressif8266\cores\esp8266\core_esp8266_features.h:50:22: note: (if you use '-fpermissive', G++ will accept your code, but allowing the use of an undeclared name is deprecated)
C:\Users\Micha\.platformio\packages\framework-arduinoespressif8266\libraries\ESP8266WiFi\src\WiFiClientSecureBearSSL.cpp: In member function 'uint8_t* BearSSL::WiFiClientSecure::_streamLoad(Stream&, size_t)':
C:\Users\Micha\.platformio\packages\framework-arduinoespressif8266\libraries\ESP8266WiFi\src\WiFiClientSecureBearSSL.cpp:1604:29: error: 'malloc' was not declared in this scope
1604 | uint8_t *dest = (uint8_t*)malloc(size);
| ^~~~~~
C:\Users\Micha\.platformio\packages\framework-arduinoespressif8266\libraries\ESP8266WiFi\src\WiFiClientSecureBearSSL.cpp:47:1: note: 'malloc' is defined in header '<cstdlib>'; did you forget to '#include <cstdlib>'?
46 | #include "coredecls.h"
+++ |+#include <cstdlib>
47 |
*** [.pio\build\esp8285\lib766\ESP8266WiFi\WiFiClientSecureBearSSL.cpp.o] Error 1