Rollup merge of #155723 - cezarbbb:fix-thumb-target-tier-spec, r=wesleywiser

Fix tier level for 5 thumb bare-metal ARM targets

The spec files for 5 Thumb-mode bare-metal ARM targets incorrectly set tier: Some(2), while the documentation correctly lists them as Tier 3. This mismatch was introduced in PR #150556 — the intent was Tier 2 eventually, but these targets should sit at Tier 3 until a proper Tier 3 → Tier 2 promotion MCP is submitted and approved.

This PR changes tier: Some(2) → Some(3) in the following spec files, making them consistent with the docs:

thumbv7a-none-eabi
thumbv7a-none-eabihf
thumbv7r-none-eabi
thumbv7r-none-eabihf
thumbv8r-none-eabihf

PS: No doc changes needed — they already correctly state Tier 3.

r?

compiler/rustc_target/src/spec/targets/thumbv7a_none_eabi.rs

@@ -7,7 +7,7 @@ pub(crate) fn target() -> Target {
         llvm_target: "thumbv7a-none-eabi".into(),
         metadata: TargetMetadata {
             description: Some("Thumb-mode Bare Armv7-A".into()),
-            tier: Some(2),
+            tier: Some(3),
             host_tools: Some(false),
             std: Some(false),
         },

compiler/rustc_target/src/spec/targets/thumbv7a_none_eabihf.rs

@@ -7,7 +7,7 @@ pub(crate) fn target() -> Target {
         llvm_target: "thumbv7a-none-eabihf".into(),
         metadata: TargetMetadata {
             description: Some("Thumb-mode Bare Armv7-A, hardfloat".into()),
-            tier: Some(2),
+            tier: Some(3),
             host_tools: Some(false),
             std: Some(false),
         },

compiler/rustc_target/src/spec/targets/thumbv7r_none_eabi.rs

@@ -7,7 +7,7 @@ pub(crate) fn target() -> Target {
         llvm_target: "thumbv7r-none-eabi".into(),
         metadata: TargetMetadata {
             description: Some("Thumb-mode Bare Armv7-R".into()),
-            tier: Some(2),
+            tier: Some(3),
             host_tools: Some(false),
             std: Some(false),
         },

compiler/rustc_target/src/spec/targets/thumbv7r_none_eabihf.rs

@@ -7,7 +7,7 @@ pub(crate) fn target() -> Target {
         llvm_target: "thumbv7r-none-eabihf".into(),
         metadata: TargetMetadata {
             description: Some("Thumb-mode Bare Armv7-R, hardfloat".into()),
-            tier: Some(2),
+            tier: Some(3),
             host_tools: Some(false),
             std: Some(false),
         },

compiler/rustc_target/src/spec/targets/thumbv8r_none_eabihf.rs

@@ -7,7 +7,7 @@ pub(crate) fn target() -> Target {
         llvm_target: "thumbv8r-none-eabihf".into(),
         metadata: TargetMetadata {
             description: Some("Thumb-mode Bare Armv8-R, hardfloat".into()),
-            tier: Some(2),
+            tier: Some(3),
             host_tools: Some(false),
             std: Some(false),
         },