Auto merge of #3534 - alyssais:musl-sched, r=JohnTitor

Provide the same sched.h constants for musl as gnu

I don't understand why these constants from Linux headers aren't just defined in linux_like/mod.rs.  Surely they'd be the same for every libc?

Author: bors

libc-test/semver/linux-musl.txt

@@ -47,6 +47,9 @@ XDP_UMEM_PGOFF_COMPLETION_RING
 XSK_UNALIGNED_BUF_OFFSET_SHIFT
 XSK_UNALIGNED_BUF_ADDR_MASK
 XDP_PKT_CONTD
+CLONE_NEWTIME
+CLONE_CLEAR_SIGHAND
+CLONE_INTO_CGROUP
 adjtimex
 aio_cancel
 aio_error

src/unix/linux_like/linux/musl/mod.rs

@@ -810,6 +810,11 @@ pub const XSK_UNALIGNED_BUF_ADDR_MASK: ::c_ulonglong = (1 << XSK_UNALIGNED_BUF_O
 
 pub const XDP_PKT_CONTD: ::__u32 = 1 << 0;
 
+// linux/sched.h
+pub const CLONE_NEWTIME: ::c_int = 0x80;
+pub const CLONE_CLEAR_SIGHAND: ::c_int = 0x100000000;
+pub const CLONE_INTO_CGROUP: ::c_int = 0x200000000;
+
 cfg_if! {
     if #[cfg(target_arch = "s390x")] {
         pub const POSIX_FADV_DONTNEED: ::c_int = 6;