Update target-spec metadata for loongarch64 targets

Author: heiher

Diff for: compiler/rustc_target/src/spec/targets/loongarch64_unknown_linux_musl.rs

@@ -4,10 +4,10 @@ pub fn target() -> Target {
     Target {
         llvm_target: "loongarch64-unknown-linux-musl".into(),
         metadata: crate::spec::TargetMetadata {
-            description: Some("LoongArch64 Linux (LP64D ABI) with musl 1.2.3".into()),
-            tier: Some(3),
-            host_tools: Some(false),
-            std: None, // ?
+            description: Some("LoongArch64 Linux (LP64D ABI) with musl 1.2.5".into()),
+            tier: Some(2),
+            host_tools: Some(true),
+            std: Some(true),
         },
         pointer_width: 64,
         data_layout: "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128".into(),

Diff for: compiler/rustc_target/src/spec/targets/loongarch64_unknown_none.rs

@@ -5,7 +5,7 @@ pub fn target() -> Target {
     Target {
         llvm_target: "loongarch64-unknown-none".into(),
         metadata: crate::spec::TargetMetadata {
-            description: None,
+            description: Some("Freestanding/bare-metal LoongArch64".into()),
             tier: Some(2),
             host_tools: Some(false),
             std: Some(false),

Diff for: compiler/rustc_target/src/spec/targets/loongarch64_unknown_none_softfloat.rs

@@ -5,7 +5,7 @@ pub fn target() -> Target {
     Target {
         llvm_target: "loongarch64-unknown-none".into(),
         metadata: crate::spec::TargetMetadata {
-            description: None,
+            description: Some("Freestanding/bare-metal LoongArch64 softfloat".into()),
             tier: Some(2),
             host_tools: Some(false),
             std: Some(false),