rustc: Add target_env for triples by default

This adds a new `#[cfg]` matcher against the `target_env` property of the
destination target triple. For example all windows triples today end with `-gnu`
but we will also hopefully support non-`gnu` targets for Windows, at which point
we'll need to differentiate between the two. This new `target_env` matches is
provided and filled in with the target's environment name.

Currently the only non-empty value of this name is `gnu`, but `musl` will be
shortly added for the linux triples.

Author: alexcrichton

src/librustc/session/config.rs

@@ -621,6 +621,7 @@ pub fn default_configuration(sess: &Session) -> ast::CrateConfig {
     let arch = &sess.target.target.arch;
     let wordsz = &sess.target.target.target_pointer_width;
     let os = &sess.target.target.target_os;
+    let env = &sess.target.target.target_env;
 
     let fam = match sess.target.target.options.is_like_windows {
         true  => InternedString::new("windows"),
@@ -634,8 +635,8 @@ pub fn default_configuration(sess: &Session) -> ast::CrateConfig {
          mk(InternedString::new("target_family"), fam),
          mk(InternedString::new("target_arch"), intern(arch)),
          mk(InternedString::new("target_endian"), intern(end)),
-         mk(InternedString::new("target_pointer_width"),
-            intern(wordsz))
+         mk(InternedString::new("target_pointer_width"), intern(wordsz)),
+         mk(InternedString::new("target_env"), intern(env)),
     ];
     if sess.opts.debug_assertions {
         ret.push(attr::mk_word_item(InternedString::new("debug_assertions")));

src/librustc_back/target/aarch64_apple_ios.rs

@@ -22,6 +22,7 @@ pub fn target() -> Target {
         target_pointer_width: "64".to_string(),
         arch: "aarch64".to_string(),
         target_os: "ios".to_string(),
+        target_env: "".to_string(),
         options: TargetOptions {
             features: "+neon,+fp-armv8,+cyclone".to_string(),
             eliminate_frame_pointer: false,

src/librustc_back/target/aarch64_linux_android.rs

@@ -24,6 +24,7 @@ pub fn target() -> Target {
         target_pointer_width: "64".to_string(),
         arch: "aarch64".to_string(),
         target_os: "android".to_string(),
+        target_env: "".to_string(),
         options: base,
     }
 }

src/librustc_back/target/aarch64_unknown_linux_gnu.rs

@@ -19,6 +19,7 @@ pub fn target() -> Target {
         llvm_target: "aarch64-unknown-linux-gnu".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
+        target_env: "gnu".to_string(),
         arch: "aarch64".to_string(),
         target_os: "linux".to_string(),
         options: base,

src/librustc_back/target/arm_linux_androideabi.rs

@@ -31,6 +31,7 @@ pub fn target() -> Target {
         target_pointer_width: "32".to_string(),
         arch: "arm".to_string(),
         target_os: "android".to_string(),
+        target_env: "gnu".to_string(),
         options: base,
     }
 }

src/librustc_back/target/arm_unknown_linux_gnueabi.rs

@@ -23,6 +23,7 @@ pub fn target() -> Target {
         target_pointer_width: "32".to_string(),
         arch: "arm".to_string(),
         target_os: "linux".to_string(),
+        target_env: "gnueabi".to_string(),
 
         options: TargetOptions {
             features: "+v6".to_string(),

src/librustc_back/target/arm_unknown_linux_gnueabihf.rs

@@ -23,6 +23,7 @@ pub fn target() -> Target {
         target_pointer_width: "32".to_string(),
         arch: "arm".to_string(),
         target_os: "linux".to_string(),
+        target_env: "gnueabihf".to_string(),
 
         options: TargetOptions {
             features: "+v6,+vfp2".to_string(),

src/librustc_back/target/armv7_apple_ios.rs

@@ -19,6 +19,7 @@ pub fn target() -> Target {
         target_pointer_width: "32".to_string(),
         arch: "arm".to_string(),
         target_os: "ios".to_string(),
+        target_env: "".to_string(),
         options: TargetOptions {
             features: "+v7,+vfp3,+neon".to_string(),
             .. opts(Arch::Armv7)

src/librustc_back/target/armv7s_apple_ios.rs

@@ -19,6 +19,7 @@ pub fn target() -> Target {
         target_pointer_width: "32".to_string(),
         arch: "arm".to_string(),
         target_os: "ios".to_string(),
+        target_env: "".to_string(),
         options: TargetOptions {
             features: "+v7,+vfp4,+neon".to_string(),
             .. opts(Arch::Armv7s)

src/librustc_back/target/i386_apple_ios.rs

@@ -23,6 +23,7 @@ pub fn target() -> Target {
         target_pointer_width: "32".to_string(),
         arch: "x86".to_string(),
         target_os: "ios".to_string(),
+        target_env: "".to_string(),
         options: opts(Arch::I386)
     }
 }