[AVR] Enable the avr-rust/llvm submodule

Author: dylanmckay

.gitmodules

@@ -1,7 +1,7 @@
 [submodule "src/llvm"]
 	path = src/llvm
-	url = https://github.com/rust-lang/llvm.git
-	branch = master
+  url = https://github.com/avr-rust/llvm.git
+	branch = avr-rust-llvm-release-4-0-1
 [submodule "src/rt/hoedown"]
 	path = src/rt/hoedown
 	url = https://github.com/rust-lang/hoedown.git

src/librustc_back/target/avr_unknown_unknown.rs

@@ -16,7 +16,7 @@ pub fn target() -> TargetResult {
         llvm_target: "avr-unknown-unknown".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "16".to_string(),
-        data_layout: "e-p:16:8-i8:8-i16:8-i32:8-i64:8-f32:8-f64:8-n8-a:8",
+        data_layout: "e-p:16:8-i8:8-i16:8-i32:8-i64:8-f32:8-f64:8-n8-a:8".to_owned(),
         arch: "avr".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         target_os: "unknown".to_string(),