libsanitizer: Avoid implicit function declaration in configure test

libsanitizer/

	* configure.ac (sanitizer_supported): Include <unistd.h> for
	syscall prototype.
	* configure: Regenerate.

libsanitizer/configure

@@ -12383,7 +12383,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 12386 "configure"
+#line 12398 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -12489,7 +12489,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 12492 "configure"
+#line 12504 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -16072,6 +16072,7 @@ case "$target" in
     cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 #include <sys/syscall.h>
+#include <unistd.h>
 int
 main ()
 {

libsanitizer/configure.ac

@@ -161,7 +161,8 @@ case "$target" in
   *-*-linux*)
     # Some old Linux distributions miss required syscalls.
     sanitizer_supported=no
-    AC_TRY_COMPILE([#include <sys/syscall.h>],[
+    AC_TRY_COMPILE([#include <sys/syscall.h>
+#include <unistd.h>],[
       syscall (__NR_gettid);
       syscall (__NR_futex);
       syscall (__NR_exit_group);