fix up cast to fix errors w/-Wstrict-prototypes

The NaCL bots use stricter warning flags and picked this up.

BUG=chromium:219015
TEST=built tests w/-Wstrict-prototypes and no longer warns
Review URL: https://codereview.chromium.org/13476002

git-svn-id: http://linux-syscall-support.googlecode.com/svn/trunk/lss@20 829466d3-f3f5-3ae4-62ad-de35cf9bba21
diff --git a/linux_syscall_support.h b/linux_syscall_support.h
index 96e4447..0bd6c53 100644
--- a/linux_syscall_support.h
+++ b/linux_syscall_support.h
@@ -2036,7 +2036,7 @@
                            "addq   $(1b-0b),%0\n"
                            : "=a" (res)
                            : "i"  (__NR_rt_sigreturn));
-      return (void (*)())(uintptr_t)res;
+      return (void (*)(void))(uintptr_t)res;
     }
   #elif defined(__ARM_ARCH_3__)
     /* Most definitions of _syscallX() neglect to mark "memory" as being