Auto merge of #38401 - redox-os:redox_cross, r=brson

Redox Cross Compilation

I will admit - there are things here that I wish I did not have to do. This completes the ability to create a cross compiler from the rust repository for `x86_64-unknown-redox`. I will document this PR with inline comments explaining some things.

[View this gist to see how a cross compiler is built](https://gist.github.com/jackpot51/6680ad973986e84d69c79854249f2b7e)

Prior discussion of a smaller change is here: #38366

Author: bors

mk/cfg/x86_64-unknown-redox.mk

@@ -0,0 +1 @@
+# rustbuild-only target

src/liballoc_jemalloc/build.rs

@@ -36,7 +36,8 @@ fn main() {
     // targets, which means we have to build the alloc_jemalloc crate
     // for targets like emscripten, even if we don't use it.
     if target.contains("rumprun") || target.contains("bitrig") || target.contains("openbsd") ||
-       target.contains("msvc") || target.contains("emscripten") || target.contains("fuchsia") {
+       target.contains("msvc") || target.contains("emscripten") || target.contains("fuchsia") ||
+       target.contains("redox") {
         println!("cargo:rustc-cfg=dummy_jemalloc");
         return;
     }

src/liballoc_system/lib.rs

@@ -19,7 +19,7 @@
             issue = "27783")]
 #![feature(allocator)]
 #![feature(staged_api)]
-#![cfg_attr(unix, feature(libc))]
+#![cfg_attr(any(unix, target_os = "redox"), feature(libc))]
 
 // The minimum alignment guaranteed by the architecture. This value is used to
 // add fast paths for low alignment values. In practice, the alignment is a
@@ -71,7 +71,7 @@ pub extern "C" fn __rust_usable_size(size: usize, align: usize) -> usize {
     imp::usable_size(size, align)
 }
 
-#[cfg(unix)]
+#[cfg(any(unix, target_os = "redox"))]
 mod imp {
     extern crate libc;
 
@@ -87,7 +87,7 @@ mod imp {
         }
     }
 
-    #[cfg(target_os = "android")]
+    #[cfg(any(target_os = "android", target_os = "redox"))]
     unsafe fn aligned_malloc(size: usize, align: usize) -> *mut u8 {
         // On android we currently target API level 9 which unfortunately
         // doesn't have the `posix_memalign` API used below. Instead we use
@@ -109,7 +109,7 @@ mod imp {
         libc::memalign(align as libc::size_t, size as libc::size_t) as *mut u8
     }
 
-    #[cfg(not(target_os = "android"))]
+    #[cfg(not(any(target_os = "android", target_os = "redox")))]
     unsafe fn aligned_malloc(size: usize, align: usize) -> *mut u8 {
         let mut out = ptr::null_mut();
         let ret = libc::posix_memalign(&mut out, align as libc::size_t, size as libc::size_t);

src/libcompiler_builtins/build.rs

@@ -242,7 +242,7 @@ fn main() {
                          "atomic_thread_fence.c"]);
     }
 
-    if !target.contains("windows") {
+    if !target.contains("redox") && !target.contains("windows") {
         sources.extend(&["emutls.c"]);
     }
 

src/liblibc

@@ -945,26 +945,20 @@ pub fn default_configuration(sess: &Session) -> ast::CrateConfig {
     let vendor = &sess.target.target.target_vendor;
     let max_atomic_width = sess.target.target.max_atomic_width();
 
-    let fam = if let Some(ref fam) = sess.target.target.options.target_family {
-        Symbol::intern(fam)
-    } else if sess.target.target.options.is_like_windows {
-        Symbol::intern("windows")
-    } else {
-        Symbol::intern("unix")
-    };
-
     let mut ret = HashSet::new();
     // Target bindings.
     ret.insert((Symbol::intern("target_os"), Some(Symbol::intern(os))));
-    ret.insert((Symbol::intern("target_family"), Some(fam)));
+    if let Some(ref fam) = sess.target.target.options.target_family {
+        ret.insert((Symbol::intern("target_family"), Some(Symbol::intern(fam))));
+        if fam == "windows" || fam == "unix" {
+            ret.insert((Symbol::intern(fam), None));
+        }
+    }
     ret.insert((Symbol::intern("target_arch"), Some(Symbol::intern(arch))));
     ret.insert((Symbol::intern("target_endian"), Some(Symbol::intern(end))));
     ret.insert((Symbol::intern("target_pointer_width"), Some(Symbol::intern(wordsz))));
     ret.insert((Symbol::intern("target_env"), Some(Symbol::intern(env))));
     ret.insert((Symbol::intern("target_vendor"), Some(Symbol::intern(vendor))));
-    if fam == "windows" || fam == "unix" {
-        ret.insert((fam, None));
-    }
     if sess.target.target.options.has_elf_tls {
         ret.insert((Symbol::intern("target_thread_local"), None));
     }

src/librustc/session/config.rs

@@ -37,6 +37,7 @@ pub fn opts() -> TargetOptions {
         function_sections: false,
         dynamic_linking: true,
         executables: true,
+        target_family: Some("unix".to_string()),
         is_like_osx: true,
         has_rpath: true,
         dll_prefix: "lib".to_string(),

src/librustc_back/target/apple_base.rs

@@ -15,6 +15,7 @@ pub fn opts() -> TargetOptions {
     TargetOptions {
         dynamic_linking: true,
         executables: true,
+        target_family: Some("unix".to_string()),
         linker_is_gnu: true,
         has_rpath: true,
         position_independent_executables: true,

src/librustc_back/target/bitrig_base.rs

@@ -15,6 +15,7 @@ pub fn opts() -> TargetOptions {
     TargetOptions {
         dynamic_linking: true,
         executables: true,
+        target_family: Some("unix".to_string()),
         linker_is_gnu: true,
         has_rpath: true,
         pre_link_args: vec![

src/librustc_back/target/dragonfly_base.rs

@@ -15,6 +15,7 @@ pub fn opts() -> TargetOptions {
     TargetOptions {
         dynamic_linking: true,
         executables: true,
+        target_family: Some("unix".to_string()),
         linker_is_gnu: true,
         has_rpath: true,
         pre_link_args: vec![