Parse error is reported for malformed body in `cfg_if!`

On the current nightly, rustfmt errors out after suggesting to add braces in an inappropriate location to a closure where it doesn't make sense to use braces begin with.

Example of affected code: https://github.com/HadrienG2/grayscott/blob/e64ff006867e7c66c9834cff20d920612578df7f/data/src/concentration/simd/safe_arch.rs#L524 .

Error message:

error: closure bodies that contain statements must be surrounded by braces
   --> /home/hadrien/Bureau/grayscott/data/src/concentration/simd/safe_arch.rs:524:45
    |
524 |                     let masks256 = array2(|i| self[i].ge(other[i]));
    |                                             ^
525 |                     let [lo128; hi128] = masks256.map(safe_arch::convert_to_m128_from_m256d);
    |                                      ^
    |
note: statement found outside of a block
   --> /home/hadrien/Bureau/grayscott/data/src/concentration/simd/safe_arch.rs:525:31
    |
524 |                     let masks256 = array2(|i| self[i].ge(other[i]));
    |                                               -------------------- this expression is a statement because of the trailing semicolon
525 |                     let [lo128; hi128] = masks256.map(safe_arch::convert_to_m128_from_m256d);
    |                               ^ this `;` turns the preceding closure into a statement
note: the closure body may be incorrectly delimited
   --> /home/hadrien/Bureau/grayscott/data/src/concentration/simd/safe_arch.rs:524:43
    |
524 |                     let masks256 = array2(|i| self[i].ge(other[i]));
    |                                           ^^^^^^^^^^^^^^^^^^^^^^^^ this is the parsed closure...
525 |                     let [lo128; hi128] = masks256.map(safe_arch::convert_to_m128_from_m256d);
    |                                      - ...but likely you meant the closure to end here
help: try adding braces
    |
524 ~                     let masks256 = array2(|i| { self[i].ge(other[i]));
525 ~                     let [lo128; hi128}] = masks256.map(safe_arch::convert_to_m128_from_m256d);
    |

Reproduce the report with the affected expression in data/src/concentration/simd/safe_arch.rs at the linked revision. Start by examining rustfmt's handling of the malformed closure body and its diagnostic suggestion. Done means the code no longer receives an inappropriate brace suggestion and reports the malformed body correctly.