Auto merge of #146 - servo:build, r=jdm

Pass -stdlib=libc++ on Apple systems

```
/Users/nox/src/mozjs/target/debug/build/mozjs_sys-0b48e14e1603d6a2/out/dist/include/mozilla/Span.h:32:10: fatal error: 'array' file not found
```

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/mozjs/146)
<!-- Reviewable:end -->

Author: bors-servo

.travis.yml

@@ -26,7 +26,7 @@ env:
 
 before_script:
   - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then export CC=gcc-6; export CXX=g++-6; fi
-  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew update; brew install [email protected] ccache yasm; fi
+  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew update; brew install [email protected] ccache llvm yasm; fi
 
 script:
   - ccache -z

Cargo.toml

@@ -2,7 +2,7 @@
 name = "mozjs_sys"
 description = "System crate for the Mozilla SpiderMonkey JavaScript engine."
 repository = "https://github.com/servo/mozjs/"
-version = "0.60.0"
+version = "0.60.1"
 authors = ["Mozilla"]
 links = "mozjs"
 build = "build.rs"

build.rs

@@ -11,7 +11,8 @@ use std::ffi::{OsStr, OsString};
 use std::process::{Command, Stdio};
 
 fn main() {
-    if cfg!(feature = "debugmozjs") && cfg!(windows) {
+    let target = env::var("TARGET").unwrap();
+    if env::var_os("CARGO_FEATURE_DEBUGMOZJS").is_some() && target.contains("windows") {
         // https://github.com/rust-lang/rust/issues/39016
         panic!("Rustc doesn't support MSVC debug runtime.");
     }
@@ -38,22 +39,23 @@ fn cc_flags() -> Vec<&'static str> {
         "-DSTATIC_JS_API",
     ];
 
-    if cfg!(feature = "debugmozjs") {
+    if env::var_os("CARGO_FEATURE_DEBUGMOZJS").is_some() {
         result.extend(&[
             "-DJS_GC_ZEAL",
             "-DDEBUG",
             "-DJS_DEBUG",
         ]);
     }
 
-    if cfg!(windows) {
+    let target = env::var("TARGET").unwrap();
+    if target.contains("windows") {
         result.extend(&[
             "-std=c++14",
             "-DWIN32",
-	    // Don't use reinterpret_cast() in offsetof(),
-	    // since it's not a constant expression, so can't
-	    // be used in static_assert().
-	    "-D_CRT_USE_BUILTIN_OFFSETOF",
+            // Don't use reinterpret_cast() in offsetof(),
+            // since it's not a constant expression, so can't
+            // be used in static_assert().
+            "-D_CRT_USE_BUILTIN_OFFSETOF",
         ]);
     } else {
         result.extend(&[
@@ -64,6 +66,13 @@ fn cc_flags() -> Vec<&'static str> {
         ]);
     }
 
+    let is_apple = target.contains("apple");
+    let is_freebsd = target.contains("freebsd");
+
+    if is_apple || is_freebsd {
+        result.push("-stdlib=libc++");
+    }
+
     result
 }
 
@@ -86,7 +95,7 @@ fn build_jsapi() {
 
     // We're using the MSYS make which doesn't work with the mingw32-make-style
     // MAKEFLAGS, so remove that from the env if present.
-    if cfg!(windows) {
+    if target.contains("windows") {
         cmd.env_remove("MAKEFLAGS").env_remove("MFLAGS");
     } else if let Some(makeflags) = env::var_os("CARGO_MAKEFLAGS") {
         cmd.env("MAKEFLAGS", makeflags);
@@ -133,8 +142,9 @@ fn build_jsglue() {
         build.flag_if_supported(flag);
     }
 
+    let target = env::var("TARGET").unwrap();
     let config = format!("{}/js/src/js-confdefs.h", out.display());
-    if cfg!(windows) {
+    if target.contains("windows") {
         build.flag("-FI");
     } else {
         build.flag("-include");
@@ -180,7 +190,8 @@ fn build_jsapi_bindings() {
         .clang_arg("-I").clang_arg(out.join("js/src").to_str().expect("UTF-8"))
         .clang_arg("-x").clang_arg("c++");
 
-    if cfg!(windows) {
+    let target = env::var("TARGET").unwrap();
+    if target.contains("windows") {
         builder = builder.clang_arg("-fms-compatibility");
     }