Auto merge of #28612 - gandro:targetvendor, r=alexcrichton

This adds a new target property, `target_vendor`. It is to be be used as a matcher for conditional compilation. The vendor is part of the [autoconf target triple](http://llvm.org/docs/doxygen/html/classllvm_1_1Triple.html#details): `<arch><sub>-<vendor>-<os>-<env>`. `arch`, `target_os` and `target_env` are already supported by Rust.

This change was suggested in PR #28593. It enables conditional compilation based on the vendor. This is needed for the rumprun target, which needs to match against both, target_os and target_vendor.

The default value for `target_vendor` is "unknown", "apple" and "pc" are other common values.

Matching against the `target_vendor` is introduced behind the feature gate `#![feature(cfg_target_vendor)]`.

This is the first time I messed around with rustc internals. I just added the my code where I found the existing `target_*` variables, hopefully I haven't missed anything. Please review with care. :)

r? @alexcrichton

Author: bors

src/doc/reference.md

@@ -2093,6 +2093,8 @@ The following configurations must be defined by the implementation:
 * `target_pointer_width = "..."` - Target pointer width in bits. This is set
   to `"32"` for targets with 32-bit pointers, and likewise set to `"64"` for
   64-bit pointers.
+* `target_vendor = "..."` - Vendor of the target, for example `apple`, `pc`, or
+  simply `"unknown"`.
 * `test` - Enabled when compiling the test harness (using the `--test` flag).
 * `unix` - See `target_family`.
 * `windows` - See `target_family`.
@@ -2269,7 +2271,7 @@ The currently implemented features of the reference compiler are:
 * `advanced_slice_patterns` - See the [match expressions](#match-expressions)
                               section for discussion; the exact semantics of
                               slice patterns are subject to change, so some types
-			      are still unstable.
+                              are still unstable.
 
 * `slice_patterns` - OK, actually, slice patterns are just scary and
                      completely unstable.
@@ -2290,6 +2292,9 @@ The currently implemented features of the reference compiler are:
 * `box_syntax` - Allows use of `box` expressions, the exact semantics of which
                  is subject to change.
 
+* `cfg_target_vendor` - Allows conditional compilation using the `target_vendor`
+                        matcher which is subject to change.
+
 * `concat_idents` - Allows use of the `concat_idents` macro, which is in many
                     ways insufficient for concatenating identifiers, and may be
                     removed entirely for something more wholesome.

src/librustc/session/config.rs

@@ -617,6 +617,7 @@ pub fn default_configuration(sess: &Session) -> ast::CrateConfig {
     let wordsz = &sess.target.target.target_pointer_width;
     let os = &sess.target.target.target_os;
     let env = &sess.target.target.target_env;
+    let vendor = &sess.target.target.target_vendor;
 
     let fam = match sess.target.target.options.is_like_windows {
         true  => InternedString::new("windows"),
@@ -632,6 +633,7 @@ pub fn default_configuration(sess: &Session) -> ast::CrateConfig {
          mk(InternedString::new("target_endian"), intern(end)),
          mk(InternedString::new("target_pointer_width"), intern(wordsz)),
          mk(InternedString::new("target_env"), intern(env)),
+         mk(InternedString::new("target_vendor"), intern(vendor)),
     ];
     if sess.opts.debug_assertions {
         ret.push(attr::mk_word_item(InternedString::new("debug_assertions")));

src/librustc_back/target/aarch64_apple_ios.rs

@@ -19,6 +19,7 @@ pub fn target() -> Target {
         arch: "aarch64".to_string(),
         target_os: "ios".to_string(),
         target_env: "".to_string(),
+        target_vendor: "apple".to_string(),
         options: TargetOptions {
             features: "+neon,+fp-armv8,+cyclone".to_string(),
             eliminate_frame_pointer: false,

src/librustc_back/target/aarch64_linux_android.rs

@@ -18,6 +18,7 @@ pub fn target() -> Target {
         arch: "aarch64".to_string(),
         target_os: "android".to_string(),
         target_env: "".to_string(),
+        target_vendor: "unknown".to_string(),
         options: super::android_base::opts(),
     }
 }

src/librustc_back/target/aarch64_unknown_linux_gnu.rs

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

src/librustc_back/target/arm_linux_androideabi.rs

@@ -21,6 +21,7 @@ pub fn target() -> Target {
         arch: "arm".to_string(),
         target_os: "android".to_string(),
         target_env: "gnu".to_string(),
+        target_vendor: "unknown".to_string(),
         options: base,
     }
 }

src/librustc_back/target/arm_unknown_linux_gnueabi.rs

@@ -19,6 +19,7 @@ pub fn target() -> Target {
         arch: "arm".to_string(),
         target_os: "linux".to_string(),
         target_env: "gnueabi".to_string(),
+        target_vendor: "unknown".to_string(),
 
         options: TargetOptions {
             features: "+v6".to_string(),

src/librustc_back/target/arm_unknown_linux_gnueabihf.rs

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