Implement the instruction_set attribute

compiler/rustc_target/src/spec/mod.rs

@@ -994,6 +994,10 @@ pub struct TargetOptions {
     /// used to locate unwinding information is passed
     /// (only has effect if the linker is `ld`-like).
     pub eh_frame_header: bool,
+
+    /// Is true if the target is an ARM architecture using thumb v1 which allows for
+    /// thumb and arm interworking.
+    pub has_thumb_interworking: bool,
 }
 
 impl Default for TargetOptions {
@@ -1086,6 +1090,7 @@ impl Default for TargetOptions {
             llvm_args: vec![],
             use_ctors_section: false,
             eh_frame_header: true,
+            has_thumb_interworking: false,
         }
     }
 }
@@ -1479,6 +1484,7 @@ impl Target {
         key!(llvm_args, list);
         key!(use_ctors_section, bool);
         key!(eh_frame_header, bool);
+        key!(has_thumb_interworking, bool);
 
         // NB: The old name is deprecated, but support for it is retained for
         // compatibility.
@@ -1717,6 +1723,7 @@ impl ToJson for Target {
         target_option_val!(llvm_args);
         target_option_val!(use_ctors_section);
         target_option_val!(eh_frame_header);
+        target_option_val!(has_thumb_interworking);
 
         if default.unsupported_abis != self.options.unsupported_abis {
             d.insert(