Auto merge of #2116 - JohnTitor:renameat2, r=Amanieu

Add `renameat2` and change their flags' type to `c_uint`

Taking over #1508. This changes the type of some flags but it should've been `c_uint`.

Closes #1508

Author: bors

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

@@ -1477,6 +1477,13 @@ extern "C" {
         offset: ::off_t,
         flags: ::c_int,
     ) -> ::ssize_t;
+    pub fn renameat2(
+        olddirfd: ::c_int,
+        oldpath: *const ::c_char,
+        newdirfd: ::c_int,
+        newpath: *const ::c_char,
+        flags: ::c_uint,
+    ) -> ::c_int;
 }
 
 extern "C" {

src/unix/linux_like/linux/mod.rs

@@ -1418,9 +1418,9 @@ pub const PTHREAD_PROCESS_PRIVATE: ::c_int = 0;
 pub const PTHREAD_PROCESS_SHARED: ::c_int = 1;
 pub const __SIZEOF_PTHREAD_COND_T: usize = 48;
 
-pub const RENAME_NOREPLACE: ::c_int = 1;
-pub const RENAME_EXCHANGE: ::c_int = 2;
-pub const RENAME_WHITEOUT: ::c_int = 4;
+pub const RENAME_NOREPLACE: ::c_uint = 1;
+pub const RENAME_EXCHANGE: ::c_uint = 2;
+pub const RENAME_WHITEOUT: ::c_uint = 4;
 
 pub const SCHED_OTHER: ::c_int = 0;
 pub const SCHED_FIFO: ::c_int = 1;