Add test of thread_local containing multiline const block

Before making thread_local accept statements inside the const block,
this test would fail to compile as follows:

    error: no rules expected the token `let`
       --> library/std/tests/thread.rs:26:13
        |
    26  |             let value = 1;
        |             ^^^ no rules expected this token in macro call
        |
    note: while trying to match meta-variable `$init:expr`
       --> library/std/src/thread/local.rs:189:69
        |
    189 |     ($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty = const { $init:expr }; $($rest:tt)*) => (
        |                                                                     ^^^^^^^^^^

0 files changed, 0 insertions, 0 deletions