librustc: Remove the fallback to `int` for integers and `f64` for

floating point numbers for real.

This will break code that looks like:

    let mut x = 0;
    while ... {
        x += 1;
    }
    println!("{}", x);

Change that code to:

    let mut x = 0i;
    while ... {
        x += 1;
    }
    println!("{}", x);

Closes #15201.

[breaking-change]

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libnum/bigint.rs b/src/libnum/bigint.rs
index 06e4792cdcc..9011aafc009 100644
--- a/src/libnum/bigint.rs
+++ b/src/libnum/bigint.rs
@@ -215,7 +215,7 @@ impl Sub<BigUint, BigUint> for BigUint {
         let zeros = ZERO_VEC.iter().cycle();
         let (a, b) = (self.data.iter().chain(zeros.clone()), other.data.iter().chain(zeros));
 
-        let mut borrow = 0;
+        let mut borrow = 0i;
         let diff: Vec<BigDigit> =  a.take(new_len).zip(b).map(|(ai, bi)| {
             let (hi, lo) = BigDigit::from_doublebigdigit(
                 BigDigit::base