Auto merge of #22532 - pnkfelix:arith-overflow, r=pnkfelix,eddyb

Rebase and follow-through on work done by @cmr and @aatch.

Implements most of rust-lang/rfcs#560. Errors encountered from the checks during building were fixed.

The checks for division, remainder and bit-shifting have not been implemented yet.

See also PR #20795

cc @Aatch ; cc @nikomatsakis

src/libcoretest/num/mod.rs

@@ -92,7 +92,7 @@ mod test {
         assert_eq!("127".parse::<i8>().ok(), Some(i8_val));
         assert_eq!("128".parse::<i8>().ok(), None);
 
-        i8_val += 1 as i8;
+        i8_val = i8_val.wrapping_add(1);
         assert_eq!("-128".parse::<i8>().ok(), Some(i8_val));
         assert_eq!("-129".parse::<i8>().ok(), None);
 
@@ -100,7 +100,7 @@ mod test {
         assert_eq!("32767".parse::<i16>().ok(), Some(i16_val));
         assert_eq!("32768".parse::<i16>().ok(), None);
 
-        i16_val += 1 as i16;
+        i16_val = i16_val.wrapping_add(1);
         assert_eq!("-32768".parse::<i16>().ok(), Some(i16_val));
         assert_eq!("-32769".parse::<i16>().ok(), None);
 
@@ -108,7 +108,7 @@ mod test {
         assert_eq!("2147483647".parse::<i32>().ok(), Some(i32_val));
         assert_eq!("2147483648".parse::<i32>().ok(), None);
 
-        i32_val += 1 as i32;
+        i32_val = i32_val.wrapping_add(1);
         assert_eq!("-2147483648".parse::<i32>().ok(), Some(i32_val));
         assert_eq!("-2147483649".parse::<i32>().ok(), None);
 
@@ -116,7 +116,7 @@ mod test {
         assert_eq!("9223372036854775807".parse::<i64>().ok(), Some(i64_val));
         assert_eq!("9223372036854775808".parse::<i64>().ok(), None);
 
-        i64_val += 1 as i64;
+        i64_val = i64_val.wrapping_add(1);
         assert_eq!("-9223372036854775808".parse::<i64>().ok(), Some(i64_val));
         assert_eq!("-9223372036854775809".parse::<i64>().ok(), None);
     }