Add esp8266 no_std target

compiler/rustc_target/src/spec/mod.rs

@@ -1794,6 +1794,7 @@ supported_targets! {
     ("xtensa-esp32s2-espidf", xtensa_esp32s2_espidf),
     ("xtensa-esp32s3-none-elf", xtensa_esp32s3_none_elf),
     ("xtensa-esp32s3-espidf", xtensa_esp32s3_espidf),
+    ("xtensa-esp8266-none-elf", xtensa_esp8266_none_elf),
 
     ("i686-wrs-vxworks", i686_wrs_vxworks),
     ("x86_64-wrs-vxworks", x86_64_wrs_vxworks),

compiler/rustc_target/src/spec/targets/xtensa_esp8266_none_elf.rs

@@ -0,0 +1,23 @@
+use crate::spec::{base::xtensa, Target, TargetOptions};
+
+pub fn target() -> Target {
+    Target {
+        llvm_target: "xtensa-none-elf".into(),
+        pointer_width: 32,
+        data_layout: "e-m:e-p:32:32-v1:8:8-i64:64-i128:128-n32".into(),
+        arch: "xtensa".into(),
+        metadata: crate::spec::TargetMetadata {
+            description: Some("Xtensa ESP8266".into()),
+            tier: Some(3),
+            host_tools: Some(false),
+            std: Some(false),
+        },
+
+        options: TargetOptions {
+            cpu: "esp8266".into(),
+            linker: Some("xtensa-lx106-elf-gcc".into()),
+            max_atomic_width: Some(32),
+            ..xtensa::opts()
+        },
+    }
+}