Migrate a few feature gate tests to ui

Renames only in this commit, and obviously
.stderr file additions.

Author: est31

src/test/compile-fail/auxiliary/cfg-target-thread-local.rs renamed to src/test/ui/auxiliary/cfg-target-thread-local.rs

@@ -0,0 +1,10 @@
+error: msp430-interrupt ABI is experimental and subject to change (see issue #38487)
+  --> $DIR/feature-gate-abi-msp430-interrupt.rs:14:1
+   |
+14 | extern "msp430-interrupt" fn foo() {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: add #![feature(abi_msp430_interrupt)] to the crate attributes to enable
+
+error: aborting due to previous error
+

src/test/compile-fail/feature-gate-abi-msp430-interrupt.rs renamed to src/test/ui/feature-gate-abi-msp430-interrupt.rs

@@ -0,0 +1,18 @@
+error: multiple-element slice matches anywhere but at the end of a slice (e.g. `[0, ..xs, 0]`) are experimental (see issue #23121)
+  --> $DIR/feature-gate-advanced-slice-features.rs:18:9
+   |
+18 |         [ xs.., 4, 5 ] => {}    //~ ERROR multiple-element slice matches
+   |         ^^^^^^^^^^^^^^
+   |
+   = help: add #![feature(advanced_slice_patterns)] to the crate attributes to enable
+
+error: multiple-element slice matches anywhere but at the end of a slice (e.g. `[0, ..xs, 0]`) are experimental (see issue #23121)
+  --> $DIR/feature-gate-advanced-slice-features.rs:19:9
+   |
+19 |         [ 1, xs.., 5 ] => {}    //~ ERROR multiple-element slice matches
+   |         ^^^^^^^^^^^^^^
+   |
+   = help: add #![feature(advanced_slice_patterns)] to the crate attributes to enable
+
+error: aborting due to 2 previous errors
+

src/test/ui/feature-gate-abi-msp430-interrupt.stderr

@@ -0,0 +1,10 @@
+error: the `#[default_lib_allocator]` attribute is an experimental feature
+  --> $DIR/feature-gate-allocator_internals.rs:11:1
+   |
+11 | #![default_lib_allocator] //~ ERROR: attribute is an experimental feature
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: add #![feature(allocator_internals)] to the crate attributes to enable
+
+error: aborting due to previous error
+