libc/pthread: fix a compilation error

libc/pthread: fix a compilation error

This patch fixes following compilation error:

    CC:  pthread/pthread_condattrsetclock.c
    pthread/pthread_condattrsetclock.c:90:5: error: function declaration isn't a prototype [-Werror=strict-prototypes]
     int pthread_condattr_setclock(attr, clock_id)
         ^
    cc1: all warnings being treated as errors
    make[1]: *** [bin/pthread_condattrsetclock.o] Error 1
    make[1]: Leaving directory `/home/ebsong/tizenrt/lib/libc'
    make: *** [libc/libc.a] Error 2

Change-Id: I1fdee78f5c3c3e2eaadaf9d7090e58794f890b64
Signed-off-by: EunBong Song <eunb.song@samsung.com>