WIP: add QNX 7.0 support for aarch64le

# Compile target

```bash
source /path/to/qnx7.0/qnxsdp-env.sh

export build_env='
    CC_aarch64-unknown-nto-qnx700=qcc
    CFLAGS_aarch64-unknown-nto-qnx700=-Vgcc_ntoaarch64le_cxx
    CXX_aarch64-unknown-nto-qnx700=qcc
    AR_aarch64_unknown_nto_qnx700=ntoaarch64-ar'

env $build_env \
    ./x.py build \
        --target x86_64-unknown-linux-gnu,aarch64-unknown-nto-qnx700 \
        rustc library/core library/alloc library/std

rustup toolchain link stage1 build/host/stage1
```

# Compile "hello world"

```bash
# In a separate terminal, without env vars

cargo new hello_world
cd hello_world
cargo +stage1 build --release --target aarch64-unknown-nto-qnx700
```

Author: nyurik

compiler/rustc_target/src/spec/mod.rs

@@ -1830,6 +1830,7 @@ supported_targets! {
 
     ("mips64-openwrt-linux-musl", mips64_openwrt_linux_musl),
 
+    ("aarch64-unknown-nto-qnx700", aarch64_unknown_nto_qnx700),
     ("aarch64-unknown-nto-qnx710", aarch64_unknown_nto_qnx710),
     ("x86_64-pc-nto-qnx710", x86_64_pc_nto_qnx710),
     ("i586-pc-nto-qnx700", i586_pc_nto_qnx700),

compiler/rustc_target/src/spec/targets/aarch64_unknown_nto_qnx700.rs

@@ -0,0 +1,41 @@
+use crate::spec::{base, Cc, LinkerFlavor, Target, TargetOptions};
+
+pub fn target() -> Target {
+    Target {
+        llvm_target: "aarch64-unknown-unknown".into(),
+        metadata: crate::spec::TargetMetadata {
+            description: Some("ARM64 QNX Neutrino 7.0 RTOS".into()),
+            tier: Some(3),
+            host_tools: Some(false),
+            std: Some(true),
+        },
+        pointer_width: 64,
+        // from: https://llvm.org/docs/LangRef.html#data-layout
+        // e         = little endian
+        // m:e       = ELF mangling: Private symbols get a .L prefix
+        // i8:8:32   = 8-bit-integer, minimum_alignment=8, preferred_alignment=32
+        // i16:16:32 = 16-bit-integer, minimum_alignment=16, preferred_alignment=32
+        // i64:64    = 64-bit-integer, minimum_alignment=64, preferred_alignment=64
+        // i128:128  = 128-bit-integer, minimum_alignment=128, preferred_alignment=128
+        // n32:64    = 32 and 64 are native integer widths; Elements of this set are considered to support most general arithmetic operations efficiently.
+        // S128      = 128 bits are the natural alignment of the stack in bits.
+        data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128-Fn32".into(),
+        arch: "aarch64".into(),
+        options: TargetOptions {
+            // TODO: need?
+            linker: Some("qcc".into()),
+            // TODO: need?
+            linker_flavor: LinkerFlavor::Unix(Cc::Yes),
+            features: "+v8a".into(),
+            max_atomic_width: Some(128),
+            pre_link_args: TargetOptions::link_args(
+                // TODO: Unix or Gnu(Yes,No)?
+                LinkerFlavor::Unix(Cc::Yes),
+                &["-Vgcc_ntoaarch64le_cxx"],
+            ),
+            // relocation_model: crate::spec::RelocModel::Pie,
+            env: "nto70".into(),
+            ..base::nto_qnx::opts()
+        },
+    }
+}

library/std/src/sys/pal/unix/fs.rs

@@ -1742,7 +1742,7 @@ pub fn link(original: &Path, link: &Path) -> io::Result<()> {
     run_path_with_cstr(original, &|original| {
         run_path_with_cstr(link, &|link| {
             cfg_if::cfg_if! {
-                if #[cfg(any(target_os = "vxworks", target_os = "redox", target_os = "android", target_os = "espidf", target_os = "horizon", target_os = "vita"))] {
+                if #[cfg(any(target_os = "vxworks", target_os = "redox", target_os = "android", target_os = "espidf", target_os = "horizon", target_os = "vita", target_os = "nto"))] {
                     // VxWorks, Redox and ESP-IDF lack `linkat`, so use `link` instead. POSIX leaves
                     // it implementation-defined whether `link` follows symlinks, so rely on the
                     // `symlink_hard_link` test in library/std/src/fs/tests.rs to check the behavior.

library/std/src/sys/pal/unix/process/process_unix.rs

@@ -24,7 +24,7 @@ use libc::{c_int, pid_t};
 use libc::{gid_t, uid_t};
 
 cfg_if::cfg_if! {
-    if #[cfg(all(target_os = "nto", target_env = "nto71"))] {
+    if #[cfg(target_os = "nto")] {
         use crate::thread;
         use libc::{c_char, posix_spawn_file_actions_t, posix_spawnattr_t};
         use crate::time::Duration;
@@ -194,7 +194,7 @@ impl Command {
     #[cfg(not(any(
         target_os = "watchos",
         target_os = "tvos",
-        all(target_os = "nto", target_env = "nto71"),
+        target_os = "nto",
     )))]
     unsafe fn do_fork(&mut self) -> Result<pid_t, io::Error> {
         cvt(libc::fork())
@@ -204,7 +204,7 @@ impl Command {
     // or closed a file descriptor while the fork() was occurring".
     // Documentation says "... or try calling fork() again". This is what we do here.
     // See also https://www.qnx.com/developers/docs/7.1/#com.qnx.doc.neutrino.lib_ref/topic/f/fork.html
-    #[cfg(all(target_os = "nto", target_env = "nto71"))]
+    #[cfg(target_os = "nto")]
     unsafe fn do_fork(&mut self) -> Result<pid_t, io::Error> {
         use crate::sys::os::errno;
 
@@ -541,7 +541,7 @@ impl Command {
         // or closed a file descriptor while the posix_spawn() was occurring".
         // Documentation says "... or try calling posix_spawn() again". This is what we do here.
         // See also http://www.qnx.com/developers/docs/7.1/#com.qnx.doc.neutrino.lib_ref/topic/p/posix_spawn.html
-        #[cfg(all(target_os = "nto", target_env = "nto71"))]
+        #[cfg(target_os = "nto")]
         unsafe fn retrying_libc_posix_spawnp(
             pid: *mut pid_t,
             file: *const c_char,

library/unwind/src/lib.rs

@@ -166,8 +166,15 @@ extern "C" {}
 extern "C" {}
 
 #[cfg(target_os = "nto")]
-#[link(name = "gcc_s")]
-extern "C" {}
+cfg_if::cfg_if! {
+    if #[cfg(target_env = "nto70")] {
+        #[link(name = "gcc")]
+        extern "C" {}
+    } else {
+        #[link(name = "gcc_s")]
+        extern "C" {}
+    }
+}
 
 #[cfg(target_os = "hurd")]
 #[link(name = "gcc_s")]

src/bootstrap/src/core/sanity.rs

@@ -38,6 +38,7 @@ pub struct Finder {
 // Targets can be removed from this list once they are present in the stage0 compiler (usually by updating the beta compiler of the bootstrap).
 #[cfg(not(feature = "bootstrap-self-test"))]
 const STAGE0_MISSING_TARGETS: &[&str] = &[
+    "aarch64-unknown-nto-qnx700"
     // just a dummy comment so the list doesn't get onelined
 ];
 

tests/assembly/targets/targets-elf.rs

@@ -54,6 +54,9 @@
 //@ revisions: aarch64_unknown_none_softfloat
 //@ [aarch64_unknown_none_softfloat] compile-flags: --target aarch64-unknown-none-softfloat
 //@ [aarch64_unknown_none_softfloat] needs-llvm-components: aarch64
+//@ revisions: aarch64_unknown_nto_qnx700
+//@ [aarch64_unknown_nto_qnx700] compile-flags: --target aarch64-unknown-nto-qnx700
+//@ [aarch64_unknown_nto_qnx700] needs-llvm-components: aarch64
 //@ revisions: aarch64_unknown_nto_qnx710
 //@ [aarch64_unknown_nto_qnx710] compile-flags: --target aarch64-unknown-nto-qnx710
 //@ [aarch64_unknown_nto_qnx710] needs-llvm-components: aarch64