Auto merge of rust-lang#127897 - nyurik:add-qnx-70-target, r=saethlin

add `aarch64_unknown_nto_qnx700` target - QNX 7.0 support for aarch64le

This backports the QNX 7.1 aarch64 implementation to 7.0.

* [x] required `-lregex` disabled, see rust-lang/libc#3775 (released in libc 0.2.156)
* [x] uses `libgcc.a` instead of `libgcc_s.so` (7.0 used ancient GCC 5.4 which didn't have gcc_s)
* [x] a fix in `backtrace` crate to support stack traces rust-lang/backtrace-rs#648

This PR bumps libc dependency to 0.2.158

CC: to the folks who did the [initial implementation](https://doc.rust-lang.org/rustc/platform-support/nto-qnx.html): `@flba-eb,` `@gh-tr,` `@jonathanpallant,` `@japaric`

# Compile target

```bash
# Configure qcc build environment
source _path_/_to_/qnx7.0/qnxsdp-env.sh

# Tell rust to use qcc when building QNX 7.0 targets
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'

# Build rust compiler, libs, and the remote test server
env $build_env ./x.py build \
  --target x86_64-unknown-linux-gnu,aarch64-unknown-nto-qnx700 \
  rustc library/core library/alloc library/std src/tools/remote-test-server

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

# Compile "hello world"

```bash
source _path_/_to_/qnx7.0/qnxsdp-env.sh

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

# Configure a remote for testing

Do this from a new shell - we will need to run more commands in the previous one.  I ran into these two issues, and found some workarounds.

* Temporary dir might not work properly
* Default `remote-test-server` has issues binding to an address

```
# ./remote-test-server
starting test server
thread 'main' panicked at src/tools/remote-test-server/src/main.rs:175:29:
called `Result::unwrap()` on an `Err` value: Os { code: 249, kind: AddrNotAvailable, message: "Can't assign requested address" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```

Specifying `--bind` param actually fixes that, and so does setting `TMPDIR` properly.

```bash
# Copy remote-test-server to remote device. You may need to use sftp instead.
# ATTENTION: Note that the path is different from the one in the remote testing documentation for some reason
scp ./build/x86_64-unknown-linux-gnu/stage1-tools-bin/remote-test-server  qnxdevice:/path/

# Run ssh with port forwarding - so that rust tester can connect to the local port instead
ssh -L 12345:127.0.0.1:12345 qnxdevice

# on the device, run
rm -rf tmp && mkdir -p tmp && TMPDIR=$PWD/tmp ./remote-test-server --bind 0.0.0.0:12345
```

# Run test suit

Assume all previous environment variables are still set, or re-init them

```bash
export TEST_DEVICE_ADDR="localhost:12345"

# tidy needs to be skipped due to using un-published libc dependency
export exclude_tests='
    --exclude src/bootstrap
    --exclude src/tools/error_index_generator
    --exclude src/tools/linkchecker
    --exclude src/tools/tidy
    --exclude tests/ui-fulldeps
    --exclude rustc
    --exclude rustdoc
    --exclude tests/run-make-fulldeps'

env $build_env ./x.py test  $exclude_tests --stage 1 --target aarch64-unknown-nto-qnx700
```

try-job: dist-x86_64-msvc

Author: bors

Diff for: std/Cargo.toml

@@ -35,7 +35,7 @@ miniz_oxide = { version = "0.7.0", optional = true, default-features = false }
 addr2line = { version = "0.22.0", optional = true, default-features = false }
 
 [target.'cfg(not(all(windows, target_env = "msvc")))'.dependencies]
-libc = { version = "0.2.153", default-features = false, features = [
+libc = { version = "0.2.156", default-features = false, features = [
     'rustc-dep-of-std',
 ], public = true }
 

Diff for: std/src/sys/pal/unix/fs.rs

@@ -1717,7 +1717,7 @@ 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.

Diff for: std/src/sys/pal/unix/process/process_unix.rs

@@ -19,7 +19,8 @@ use crate::sys::process::process_common::*;
 use crate::{fmt, mem, sys};
 
 cfg_if::cfg_if! {
-    if #[cfg(all(target_os = "nto", target_env = "nto71"))] {
+    // This workaround is only needed for QNX 7.0 and 7.1. The bug should have been fixed in 8.0
+    if #[cfg(any(target_env = "nto70", target_env = "nto71"))] {
         use crate::thread;
         use libc::{c_char, posix_spawn_file_actions_t, posix_spawnattr_t};
         use crate::time::Duration;
@@ -189,7 +190,8 @@ impl Command {
     #[cfg(not(any(
         target_os = "watchos",
         target_os = "tvos",
-        all(target_os = "nto", target_env = "nto71"),
+        target_env = "nto70",
+        target_env = "nto71"
     )))]
     unsafe fn do_fork(&mut self) -> Result<pid_t, io::Error> {
         cvt(libc::fork())
@@ -199,7 +201,8 @@ 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"))]
+    // This workaround is only needed for QNX 7.0 and 7.1. The bug should have been fixed in 8.0
+    #[cfg(any(target_env = "nto70", target_env = "nto71"))]
     unsafe fn do_fork(&mut self) -> Result<pid_t, io::Error> {
         use crate::sys::os::errno;
 
@@ -537,7 +540,7 @@ 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,

Diff for: unwind/src/lib.rs

@@ -165,8 +165,15 @@ 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")]