Changing Name of a thread

[Keywan Ghadami via Digitalmars-d-learn]

Hello, i am trying to the set the name of thread with:

     import core.thread;
     auto thisThread = Thread.getThis();
     thisThread.name = "kiwi";

but GDB prints the name of the programm ("helloworld")

     [Thread debugging using libthread_db enabled]
     Using host libthread_db library 
"/lib/x86_64-linux-gnu/libthread_db.so.1".
     Edit source/app.d to start your project.
     ^C
     Program received signal SIGINT, Interrupt.
     D main () at source/app.d:17
     17		}
     (gdb) info threads
       Id   Target Id         Frame
     * 1    Thread 0x7ffff7fd0800 (LWP 3232) "helloworld" D main 
() at source/app.d:17

Next thing i tried was calling pthread_setname_np (Linux) but it 
seams that is not defined in phobos, so i tried to delcare it by 
my self:

     import core.sys.posix.pthread;
     import std.string;
     extern(C) int pthread_setname_np(pthread_t, const char*);
     pthread_setname_np(pthread_self(), toStringz("thread_name"));

but this gives me
    helloworld ~master: building configuration "application"...
    dmd -c 
-of.dub/build/application-debug-linux.posix-x86_64-dmd_2069-AAC406C4728034581B43AEC547EAA8E7/helloworld.o -debug -g -w -version=Have_helloworld -Isource/ source/app.d source/kiwi.d -vcolumns
    Linking...
    dmd 
-of.dub/build/application-debug-linux.posix-x86_64-dmd_2069-AAC406C4728034581B43AEC547EAA8E7/helloworld .dub/build/application-debug-linux.posix-x86_64-dmd_2069-AAC406C4728034581B43AEC547EAA8E7/helloworld.o -L--no-as-needed -g
    
.dub/build/application-debug-linux.posix-x86_64-dmd_2069-AAC406C4728034581B43AEC547EAA8E7/helloworld.o: In function `_Dmain':
/home/keywan/hello_world/source/app.d:13: undefined reference to 
`_D3app4mainFZ18pthread_setname_npUmxPaZi'
    collect2: error: ld returned 1 exit status
    --- errorlevel 1
    FAIL 
.dub/build/application-debug-linux.posix-x86_64-dmd_2069-AAC406C4728034581B43AEC547EAA8E7/ helloworld executable
    dmd failed with exit code 1.

sorry for asking stupid questions but my background is more 
PHP,Perl,Java...
any help would be appreciated. (context i am trying to make 
debugging easier by giving the threads names)