sparc: fix build of gdb/testsuite/gdb.arch/sparc-sysstep.c

This patch adds a missing include that makes the test program to not
be built (--Wimplicit-function-declaration).

gdb/testsuite/ChangeLog:

2015-11-20  Jose E. Marchesi  <jose.marchesi@oracle.com>

    	* gdb.arch/sparc-sysstep.c: Include unistd.h for getpid.

gdb/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2015-11-20  Jose E. Marchesi  <jose.marchesi@oracle.com>
+
+    	* gdb.arch/sparc-sysstep.c: Include unistd.h for getpid.
+
 2015-11-19  Sandra Loosemore  <sandra@codesourcery.com>
 
 	* gdb.base/nested-subp1.exp: Pass executable, not executable name,

gdb/testsuite/gdb.arch/sparc-sysstep.c

@@ -18,6 +18,7 @@
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
 #include <signal.h>
+#include <unistd.h>
 
 int global;