SDK version is 54.16 (22.08.2022) [problem solved]

g++ -c -D__USE_INLINE__ -I./ -I../ vector.cpp -o vector.o
g++ -c -D__USE_INLINE__ -I./ -I../ pointer.cpp -o pointer.o
g++ -c -D__USE_INLINE__ -I./ -I../ undo.cpp -o undo.o
g++ -c -D__USE_INLINE__ -I./ -I../ iconify.cpp -o iconify.o
g++ init.o tools/rnd.o tools/plot.o tools/draw.o tools/line.o tools/curv.o tools/box.o tools/bar.o tools/circle.o tools/ellipse.o tools/cut.o tools/paste.o tools/symmetri.o tools/filledcircle.o tools/fill.o toolbox.o pen.o main.o vector.o pointer.o undo.o iconify.o -o ldpaint
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libstdc++.a(eh_alloc.o): In function `__gnu_cxx::__mutex::lock()':
/opt/adtools/native-build/gcc-native-build-8.4.0/ppc-amigaos/libstdc++-v3/include/ext/concurrence.h:150: undefined reference to `__gthread_active_p'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libstdc++.a(eh_alloc.o): In function `__gnu_cxx::__mutex::unlock()':
/opt/adtools/native-build/gcc-native-build-8.4.0/ppc-amigaos/libstdc++-v3/include/ext/concurrence.h:161: undefined reference to `__gthread_active_p'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libstdc++.a(eh_alloc.o): In function `free':
/opt/adtools/native-build/gcc-native-build-8.4.0/ppc-amigaos/libstdc++-v3/include/ext/concurrence.h:152: undefined reference to `__gthread_mutex_lock'
/opt/adtools/native-build/gcc-native-build-8.4.0/ppc-amigaos/libstdc++-v3/include/ext/concurrence.h:163: undefined reference to `__gthread_mutex_unlock'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libstdc++.a(eh_alloc.o): In function `__gnu_cxx::__mutex::lock()':
/opt/adtools/native-build/gcc-native-build-8.4.0/ppc-amigaos/libstdc++-v3/include/ext/concurrence.h:150: undefined reference to `__gthread_active_p'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libstdc++.a(eh_alloc.o): In function `__gnu_cxx::__mutex::unlock()':
/opt/adtools/native-build/gcc-native-build-8.4.0/ppc-amigaos/libstdc++-v3/include/ext/concurrence.h:161: undefined reference to `__gthread_active_p'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libstdc++.a(eh_alloc.o): In function `allocate':
/opt/adtools/native-build/gcc-native-build-8.4.0/ppc-amigaos/libstdc++-v3/include/ext/concurrence.h:152: undefined reference to `__gthread_mutex_lock'
/opt/adtools/native-build/gcc-native-build-8.4.0/ppc-amigaos/libstdc++-v3/include/ext/concurrence.h:163: undefined reference to `__gthread_mutex_unlock'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libstdc++.a(eh_alloc.o): In function `_GLOBAL__sub_I_eh_alloc.cc':
/opt/adtools/native-build/gcc-native-build-8.4.0/ppc-amigaos/libstdc++-v3/include/ext/concurrence.h:134: undefined reference to `__gthread_active_p'
/opt/adtools/native-build/gcc-native-build-8.4.0/ppc-amigaos/libstdc++-v3/include/ext/concurrence.h:135: undefined reference to `__gthread_mutex_init'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libstdc++.a(eh_alloc.o): In function `_ZN9__gnu_cxx7__mutexD4Ev':
/opt/adtools/native-build/gcc-native-build-8.4.0/ppc-amigaos/libstdc++-v3/include/ext/concurrence.h:142: undefined reference to `__gthread_active_p'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libstdc++.a(eh_alloc.o): In function `_GLOBAL__sub_D_eh_alloc.cc':
/opt/adtools/native-build/gcc-native-build-8.4.0/ppc-amigaos/libstdc++-v3/include/ext/concurrence.h:143: undefined reference to `__gthread_mutex_destroy'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libstdc++.a(eh_globals.o): In function `__cxa_get_globals_fast':
/opt/adtools/gcc/repo/libstdc++-v3/libsupc++/eh_globals.cc:116: undefined reference to `__gthread_getspecific'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libstdc++.a(eh_globals.o): In function `__cxa_get_globals':
/opt/adtools/gcc/repo/libstdc++-v3/libsupc++/eh_globals.cc:128: undefined reference to `__gthread_getspecific'
/opt/adtools/gcc/repo/libstdc++-v3/libsupc++/eh_globals.cc:132: undefined reference to `__gthread_setspecific'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libstdc++.a(eh_globals.o): In function `_GLOBAL__sub_I_eh_globals.cc':
/opt/adtools/gcc/repo/libstdc++-v3/libsupc++/eh_globals.cc:97: undefined reference to `__gthread_active_p'
/opt/adtools/gcc/repo/libstdc++-v3/libsupc++/eh_globals.cc:98: undefined reference to `__gthread_key_create'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libstdc++.a(eh_globals.o): In function `_GLOBAL__sub_D_eh_globals.cc':
/opt/adtools/gcc/repo/libstdc++-v3/libsupc++/eh_globals.cc:104: undefined reference to `__gthread_key_delete'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libgcc_eh.a(unwind-sjlj.o): In function `fc_key_init_once':
/opt/adtools/gcc/repo/libgcc/unwind-sjlj.c:114: undefined reference to `__gthread_once'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libgcc_eh.a(unwind-sjlj.o): In function `fc_key_init':
/opt/adtools/gcc/repo/libgcc/unwind-sjlj.c:107: undefined reference to `__gthread_key_create'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libgcc_eh.a(unwind-sjlj.o): In function `uw_install_context':
/opt/adtools/gcc/repo/libgcc/unwind-sjlj.c:160: undefined reference to `__gthread_setspecific'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libgcc_eh.a(unwind-sjlj.o): In function `_Unwind_ForcedUnwind_Phase2':
/opt/adtools/gcc/repo/libgcc/unwind-sjlj.c:160: undefined reference to `__gthread_setspecific'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libgcc_eh.a(unwind-sjlj.o): In function `_Unwind_SjLj_Register':
/opt/adtools/gcc/repo/libgcc/unwind-sjlj.c:128: undefined reference to `__gthread_getspecific'
/opt/adtools/gcc/repo/libgcc/unwind-sjlj.c:129: undefined reference to `__gthread_setspecific'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libgcc_eh.a(unwind-sjlj.o): In function `_Unwind_SjLj_Unregister':
/opt/adtools/gcc/repo/libgcc/unwind-sjlj.c:160: undefined reference to `__gthread_setspecific'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libgcc_eh.a(unwind-sjlj.o): In function `_Unwind_SjLj_RaiseException':
/opt/adtools/gcc/repo/libgcc/unwind-sjlj.c:147: undefined reference to `__gthread_getspecific'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libgcc_eh.a(unwind-sjlj.o): In function `_Unwind_SjLj_ForcedUnwind':
/opt/adtools/gcc/repo/libgcc/unwind-sjlj.c:147: undefined reference to `__gthread_getspecific'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libgcc_eh.a(unwind-sjlj.o): In function `_Unwind_SjLj_Resume':
/opt/adtools/gcc/repo/libgcc/unwind-sjlj.c:147: undefined reference to `__gthread_getspecific'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libgcc_eh.a(unwind-sjlj.o): In function `_Unwind_SjLj_Resume_or_Rethrow':
/opt/adtools/gcc/repo/libgcc/unwind-sjlj.c:147: undefined reference to `__gthread_getspecific'
/GCC/lib/gcc/ppc-amigaos/8.4.0/newlib/lib/libgcc_eh.a(unwind-sjlj.o): In function `_Unwind_Backtrace':
/opt/adtools/gcc/repo/libgcc/unwind-sjlj.c:147: undefined reference to `__gthread_getspecific'
make: *** [all] Error 1
6.Work:pro_2023/ldpaint>

@LiveForIt

adding -lpthread did not help
SDK version is 54.16 (22.08.2022)

@LiveForIt

needed to add -athread=native at end of the linking stage.

Thanks to rjd324