check for pthread_setname_np incorrectly fails

scons: Configure: Checking if pthread_setname_np is supported... 

build/opt/scons/sconf_temp/conftest_49.cpp <-

  |

  |#define _GNU_SOURCE

  |#include <pthread.h>

  |

  |int main() {

  |    pthread_setname_np(pthread_self(), "test");

  |    return 0;

  |}

  |

Compiling build/opt/scons/sconf_temp/conftest_49.o

build/opt/scons/sconf_temp/conftest_49.cpp:2:0: error: "_GNU_SOURCE" redefined [-Werror]

 #define _GNU_SOURCE

<command-line>:0:0: note: this is the location of the previous definition

cc1plus: all warnings being treated as errors

scons: Configure: no