Enable #[thread_local] on armv6k-nintendo-3ds

Since libctru 2.1.2 was released
(https://github.com/devkitPro/libctru/releases/tag/v2.1.2) we should be
able to use real #[thread_local] without corruption issues on the 3DS
target.

Author: ian-h-chamberlain

compiler/rustc_target/src/spec/armv6k_nintendo_3ds.rs

@@ -29,8 +29,7 @@ pub fn target() -> Target {
             pre_link_args,
             exe_suffix: ".elf".into(),
             no_default_libraries: false,
-            // There are some issues in debug builds with this enabled in certain programs.
-            has_thread_local: false,
+            has_thread_local: true,
             ..Default::default()
         },
     }