refactor build.rs to not depend on rustc-cfg

it now uses the CARGO_CFG_TARGET variables provided by Cargo

Cargo.toml

@@ -4,9 +4,6 @@ build = "build.rs"
 name = "compiler_builtins"
 version = "0.1.0"
 
-[build-dependencies]
-rustc-cfg = "0.3.0"
-
 [build-dependencies.gcc]
 optional = true
 version = "0.3.36"

build.rs

@@ -1,23 +1,50 @@
+use std::env;
+
+fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+
+    let target = env::var("TARGET").unwrap();
+
+    // Emscripten's runtime includes all the builtins
+    if target.contains("emscripten") {
+        return;
+    }
+
+    // NOTE we are going to assume that llvm-target, what determines our codegen option, matches the
+    // target triple. This is usually correct for our built-in targets but can break in presence of
+    // custom targets, which can have arbitrary names.
+    let llvm_target = target.split('-').collect::<Vec<_>>();
+
+    // Build missing intrinsics from compiler-rt C source code
     #[cfg(feature = "c")]
+    c::compile(&llvm_target);
+
+    // To compile intrinsics.rs for thumb targets, where there is no libc
+    if llvm_target[0].starts_with("thumb") {
+        println!("cargo:rustc-cfg=thumb")
+    }
+
+    // compiler-rt `cfg`s away some intrinsics for thumbv6m because that target doesn't have full
+    // THUMBv2 support. We have to cfg our code accordingly.
+    if llvm_target[0] == "thumbv6m" {
+        println!("cargo:rustc-cfg=thumbv6m")
+    }
+}
+
+#[cfg(feature = "c")]
+mod c {
     extern crate gcc;
-extern crate rustc_cfg;
 
-#[cfg(feature = "c")]
     use std::collections::BTreeMap;
+    use std::env;
     use std::io::Write;
-#[cfg(feature = "c")]
     use std::path::Path;
-use std::{env, io, process};
 
-use rustc_cfg::Cfg;
-
-#[cfg(feature = "c")]
     struct Sources {
         // SYMBOL -> PATH TO SOURCE
         map: BTreeMap<&'static str, &'static str>,
     }
 
-#[cfg(feature = "c")]
     impl Sources {
         fn new() -> Sources {
             Sources { map: BTreeMap::new() }
@@ -51,31 +78,13 @@ impl Sources {
         }
     }
 
-fn main() {
+    /// Compile intrinsics from the compiler-rt C source code
-    println!("cargo:rerun-if-changed=build.rs");
+    pub fn compile(llvm_target: &[&str]){
+        let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap();
+        let target_env = env::var("CARGO_CFG_TARGET_ENV").unwrap();
+        let target_os = env::var("CARGO_CFG_TARGET_OS").unwrap();
+        let target_vendor = env::var("CARGO_CFG_TARGET_VENDOR").unwrap();
 
-    let target = env::var("TARGET").unwrap();
-
-    // Emscripten's runtime includes all the builtins
-    if target.contains("emscripten") {
-        return;
-    }
-
-    let Cfg { ref target_arch, ref target_os, ref target_env, ref target_vendor, .. } =
-        Cfg::new(&target).unwrap_or_else(|e| {
-            writeln!(io::stderr(), "{}", e).ok();
-            process::exit(1)
-        });
-    // NOTE we are going to assume that llvm-target, what determines our codegen option, matches the
-    // target triple. This is usually correct for our built-in targets but can break in presence of
-    // custom targets, which can have arbitrary names.
-    let llvm_target = target.split('-').collect::<Vec<_>>();
-
-    // Build missing intrinsics from compiler-rt C source code
-    match () {
-        #[cfg(feature = "c")]
-        () => {
-            let target_vendor = target_vendor.as_ref().unwrap();
         let cfg = &mut gcc::Config::new();
 
         if target_env == "msvc" {
@@ -404,7 +413,7 @@ fn main() {
             Path::new(".")
         };
 
-            let src_dir = root.join("compiler-rt/compiler-rt-cdylib/compiler-rt/lib/builtins");
+        let src_dir = root.join("c/compiler-rt/lib/builtins");
         for src in sources.map.values() {
             let src = src_dir.join(src);
             cfg.file(&src);
@@ -413,24 +422,4 @@ fn main() {
 
         cfg.compile("libcompiler-rt.a");
     }
-        #[cfg(not(feature = "c"))]
-        () => {}
-    }
-
-    // To filter away some flaky test (see src/float/add.rs for details)
-    if llvm_target[0].starts_with("arm") &&
-       llvm_target.last().unwrap().contains("gnueabi") {
-        println!("cargo:rustc-cfg=arm_linux")
-    }
-
-    // To compile intrinsics.rs for thumb targets, where there is no libc
-    if llvm_target[0].starts_with("thumb") {
-        println!("cargo:rustc-cfg=thumb")
-    }
-
-    // compiler-rt `cfg`s away some intrinsics for thumbv6m because that target doesn't have full
-    // THUMBv2 support. We have to cfg our code accordingly.
-    if llvm_target[0] == "thumbv6m" {
-        println!("cargo:rustc-cfg=thumbv6m")
-    }
 }