Make MachBackend::triple return &Triple

This avoids an unnecessary clone

cranelift/codegen/src/isa/aarch64/mod.rs

@@ -98,8 +98,8 @@ impl MachBackend for AArch64Backend {
         "aarch64"
     }
 
-    fn triple(&self) -> Triple {
-        self.triple.clone()
+    fn triple(&self) -> &Triple {
+        &self.triple
     }
 
     fn flags(&self) -> &shared_settings::Flags {

cranelift/codegen/src/isa/arm32/mod.rs

@@ -88,8 +88,8 @@ impl MachBackend for Arm32Backend {
         "arm32"
     }
 
-    fn triple(&self) -> Triple {
-        self.triple.clone()
+    fn triple(&self) -> &Triple {
+        &self.triple
     }
 
     fn flags(&self) -> &settings::Flags {

cranelift/codegen/src/isa/s390x/mod.rs

@@ -101,8 +101,8 @@ impl MachBackend for S390xBackend {
         "s390x"
     }
 
-    fn triple(&self) -> Triple {
-        self.triple.clone()
+    fn triple(&self) -> &Triple {
+        &self.triple
     }
 
     fn flags(&self) -> &shared_settings::Flags {

cranelift/codegen/src/isa/x64/mod.rs

@@ -98,8 +98,8 @@ impl MachBackend for X64Backend {
         "x64"
     }
 
-    fn triple(&self) -> Triple {
-        self.triple.clone()
+    fn triple(&self) -> &Triple {
+        &self.triple
     }
 
     fn reg_universe(&self) -> &RealRegUniverse {