Don't cast thread name to an integer for prctl

libc::prctl and the prctl definitions in glibc, musl, and the kernel
headers are C variadic functions. Therefore, all the arguments (except
for the first) are untyped. It is only the Linux man page which says
that prctl takes 4 unsigned long arguments. I have no idea why it says
this.

In any case, the upshot is that we don't need to cast the pointer to an
integer and confuse Miri.

Author: saethlin

library/std/src/sys/unix/thread.rs

@@ -122,7 +122,7 @@ impl Thread {
         // pthread wrapper only appeared in glibc 2.12, so we use syscall
         // directly.
         unsafe {
-            libc::prctl(PR_SET_NAME, name.as_ptr() as libc::c_ulong, 0, 0, 0);
+            libc::prctl(PR_SET_NAME, name.as_ptr(), 0, 0, 0);
         }
     }