Build warnings since glibc-2.43

[heitbaum]

In constructor 'libconfig::SettingException::SettingException(const char*)',
    inlined from 'libconfig::SettingNotFoundException::SettingNotFoundException(const char*)' at libconfigcpp.c++:314:26,
    inlined from 'const libconfig::Setting& libconfig::Setting::getParent() const' at libconfigcpp.c++:1132:40:
libconfigcpp.c++:195:19: warning: argument 1 null where non-null expected [-Wnonnull]
  195 |   _path = ::strdup(path);
      |           ~~~~~~~~^~~~~~
In file included from /var/media/DATA/home-rudi/LibreELEC.tv/build.LibreELEC-Generic.x86_64-13.0-devel/toolchain/x86_64-libreelec-linux-gnu/include/c++/16.0.1/cstring:48,
                 from libconfigcpp.c++:34:
/var/media/DATA/home-rudi/LibreELEC.tv/build.LibreELEC-Generic.x86_64-13.0-devel/toolchain/x86_64-libreelec-linux-gnu/sysroot/usr/include/string.h: In function 'const libconfig::Setting& libconfig::Setting::getParent() const':
/var/media/DATA/home-rudi/LibreELEC.tv/build.LibreELEC-Generic.x86_64-13.0-devel/toolchain/x86_64-libreelec-linux-gnu/sysroot/usr/include/string.h:202:14: note: in a call to function 'char* strdup(const char*)' declared 'nonnull'
  202 | extern char *strdup (const char *__s)
      |              ^~~~~~
In constructor 'libconfig::SettingException::SettingException(const char*)',
    inlined from 'libconfig::SettingNotFoundException::SettingNotFoundException(const char*)' at libconfigcpp.c++:314:26,
    inlined from 'libconfig::Setting& libconfig::Setting::getParent()' at libconfigcpp.c++:1144:40:
libconfigcpp.c++:195:19: warning: argument 1 null where non-null expected [-Wnonnull]
  195 |   _path = ::strdup(path);
      |           ~~~~~~~~^~~~~~
/var/media/DATA/home-rudi/LibreELEC.tv/build.LibreELEC-Generic.x86_64-13.0-devel/toolchain/x86_64-libreelec-linux-gnu/sysroot/usr/include/string.h: In member function 'libconfig::Setting& libconfig::Setting::getParent()':
/var/media/DATA/home-rudi/LibreELEC.tv/build.LibreELEC-Generic.x86_64-13.0-devel/toolchain/x86_64-libreelec-linux-gnu/sysroot/usr/include/string.h:202:14: note: in a call to function 'char* strdup(const char*)' declared 'nonnull'
  202 | extern char *strdup (const char *__s)
      |              ^~~~~~