Fix integers in tests (fixup #22700)

Author: Manishearth

Diff for: src/libstd/sync/mpsc/select.rs

@@ -473,7 +473,7 @@ mod test {
 
     #[test]
     fn stress() {
-        static AMT: u32 = 10000;
+        static AMT: i32 = 10000;
         let (tx1, rx1) = channel::<i32>();
         let (tx2, rx2) = channel::<i32>();
         let (tx3, rx3) = channel::<()>();

Diff for: src/libstd/sync/rwlock.rs

@@ -425,8 +425,8 @@ mod tests {
     #[test]
     fn frob() {
         static R: StaticRwLock = RW_LOCK_INIT;
-        static N: u32 = 10;
-        static M: u32 = 1000;
+        static N: usize = 10;
+        static M: usize = 1000;
 
         let (tx, rx) = channel::<()>();
         for _ in 0..N {

Diff for: src/libstd/sync/task_pool.rs

@@ -142,7 +142,7 @@ mod test {
     use super::*;
     use sync::mpsc::channel;
 
-    const TEST_TASKS: u32 = 4;
+    const TEST_TASKS: usize = 4;
 
     #[test]
     fn test_works() {