[AVR][No Upstream] Expose the 'target_cpu' feature flag

src/librustc/session/config.rs

@@ -1397,6 +1397,7 @@ pub fn default_lib_output() -> CrateType {
 pub fn default_configuration(sess: &Session) -> ast::CrateConfig {
     let end = &sess.target.target.target_endian;
     let arch = &sess.target.target.arch;
+    let cpu = &sess.target.target.options.cpu;
     let wordsz = &sess.target.target.target_pointer_width;
     let os = &sess.target.target.target_os;
     let env = &sess.target.target.target_env;
@@ -1426,6 +1427,10 @@ pub fn default_configuration(sess: &Session) -> ast::CrateConfig {
         Symbol::intern("target_vendor"),
         Some(Symbol::intern(vendor)),
     ));
+    if sess.target.target.options.is_specific_cpu() {
+        ret.insert((Symbol::intern("target_cpu"), Some(Symbol::intern(cpu))));
+    }
+
     if sess.target.target.options.has_elf_tls {
         ret.insert((Symbol::intern("target_thread_local"), None));
     }

src/librustc_target/spec/mod.rs

@@ -788,6 +788,12 @@ impl Default for TargetOptions {
     }
 }
 
+impl TargetOptions {
+    pub fn is_specific_cpu(&self) -> bool {
+        self.cpu != "generic"
+    }
+}
+
 impl Target {
     /// Given a function ABI, turn it into the correct ABI for this target.
     pub fn adjust_abi(&self, abi: Abi) -> Abi {

src/test/run-pass/cfg-target-cpu.rs

@@ -0,0 +1,18 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+pub fn main() {
+    if cfg!(target_cpu = "cortex-a8") {
+        println!("Running on Cortex A8!");
+    } else {
+        println!("Running on an arbitrary cpu");
+    }
+}
+