Small fixme in core now that split_first has no codegen issues

Author: GrigorenkoPV

library/core/src/num/dec2flt/common.rs

@@ -39,9 +39,7 @@ impl ByteSlice for [u8] {
     fn parse_digits(&self, mut func: impl FnMut(u8)) -> &Self {
         let mut s = self;
 
-        // FIXME: Can't use s.split_first() here yet,
-        // see https://github.com/rust-lang/rust/issues/109328
-        while let [c, s_next @ ..] = s {
+        while let Some((c, s_next)) = s.split_first() {
             let c = c.wrapping_sub(b'0');
             if c < 10 {
                 func(c);

library/core/src/num/dec2flt/parse.rs

@@ -51,9 +51,7 @@ fn try_parse_19digits(s_ref: &mut &[u8], x: &mut u64) {
     let mut s = *s_ref;
 
     while *x < MIN_19DIGIT_INT {
-        // FIXME: Can't use s.split_first() here yet,
-        // see https://github.com/rust-lang/rust/issues/109328
-        if let [c, s_next @ ..] = s {
+        if let Some((c, s_next)) = s.split_first() {
             let digit = c.wrapping_sub(b'0');
 
             if digit < 10 {