Introduce prototype-style function definition for timespec_get.

Upstream, this was part of this commit:

commit f534255e4d276ee7b20b45637d16a00b122e5df3

Author: Adhemerval Zanella <adhemerval.zanella@linaro.com>

Date:   Fri Apr 17 10:58:31 2015 -0300

    Consolidate vDSO macros and usage

diff --git a/sysdeps/unix/sysv/linux/timespec_get.c b/sysdeps/unix/sysv/linux/timespec_get.c

index b037abee20c7d30c..8c5c8eae0cc0e579 100644

--- a/sysdeps/unix/sysv/linux/timespec_get.c

+++ b/sysdeps/unix/sysv/linux/timespec_get.c

@@ -34,9 +34,7 @@

 /* Set TS to calendar time based in time base BASE.  */

 int

-timespec_get (ts, base)

-     struct timespec *ts;

-     int base;

+timespec_get (struct timespec *ts, int base)

 {

   switch (base)

     {