add thread_local! example to the feature gate test

Author: folkertdev

tests/ui/feature-gates/feature-gate-static_align.rs

@@ -9,3 +9,11 @@ extern "C" {
     //~^ ERROR the `#[rustc_align_static]` attribute is an experimental feature
     static FOREIGN_STATIC: u32;
 }
+
+// NOTE: the error is reported twice because the expansion of `thread_local` contains 2 statics.
+thread_local! {
+    //~^ ERROR the `#[rustc_align_static]` attribute is an experimental feature
+    //~| ERROR the `#[rustc_align_static]` attribute is an experimental feature
+    #[rustc_align_static(16)]
+    static THREAD_LOCAL: u16 = 0;
+}

tests/ui/feature-gates/feature-gate-static_align.stderr

@@ -18,6 +18,38 @@ LL |     #[rustc_align_static(16)]
    = help: add `#![feature(static_align)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error: aborting due to 2 previous errors
+error[E0658]: the `#[rustc_align_static]` attribute is an experimental feature
+  --> $DIR/feature-gate-static_align.rs:14:1
+   |
+LL | / thread_local! {
+LL | |
+LL | |
+LL | |     #[rustc_align_static(16)]
+LL | |     static THREAD_LOCAL: u16 = 0;
+LL | | }
+   | |_^
+   |
+   = note: see issue #146177 <https://github.com/rust-lang/rust/issues/146177> for more information
+   = help: add `#![feature(static_align)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+   = note: this error originates in the macro `$crate::thread::local_impl::thread_local_inner` which comes from the expansion of the macro `thread_local` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0658]: the `#[rustc_align_static]` attribute is an experimental feature
+  --> $DIR/feature-gate-static_align.rs:14:1
+   |
+LL | / thread_local! {
+LL | |
+LL | |
+LL | |     #[rustc_align_static(16)]
+LL | |     static THREAD_LOCAL: u16 = 0;
+LL | | }
+   | |_^
+   |
+   = note: see issue #146177 <https://github.com/rust-lang/rust/issues/146177> for more information
+   = help: add `#![feature(static_align)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+   = note: this error originates in the macro `$crate::thread::local_impl::thread_local_inner` which comes from the expansion of the macro `thread_local` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0658`.