fixup! std: add platform support for hexagon-unknown-qurt

- Add errno_location link_name for QuRT (_Geterrno)
- Enable unix stdio path for QuRT (remove not(target_os = "qurt") gate)
- Exclude getppid export on QuRT (no process spawning support)
- Fix link() match arms to return Ok(()) from each branch

Author: androm3da

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

@@ -2205,7 +2205,7 @@ pub fn link(original: &CStr, link: &CStr) -> io::Result<()> {
         target_os = "qurt" => {
             // QuRT doesn't support hard links
             let _ = (original, link);
-            return Err(io::const_error!(io::ErrorKind::Unsupported, "link not supported on QuRT"));
+            Err(io::const_error!(io::ErrorKind::Unsupported, "link not supported on QuRT"))
         }
         any(
             // VxWorks, Redox and ESP-IDF lack `linkat`, so use `link` instead.
@@ -2224,14 +2224,15 @@ pub fn link(original: &CStr, link: &CStr) -> io::Result<()> {
             target_env = "nto70",
         ) => {
             cvt(unsafe { libc::link(original.as_ptr(), link.as_ptr()) })?;
+            Ok(())
         }
         _ => {
             // Where we can, use `linkat` instead of `link`; see the comment above
             // this one for details on why.
             cvt(unsafe { libc::linkat(libc::AT_FDCWD, original.as_ptr(), libc::AT_FDCWD, link.as_ptr(), 0) })?;
+            Ok(())
         }
     }
-    Ok(())
 }
 
 pub fn stat(p: &CStr) -> io::Result<FileAttr> {

library/std/src/sys/io/error/unix.rs

@@ -30,6 +30,7 @@ unsafe extern "C" {
     #[cfg_attr(any(target_os = "freebsd", target_vendor = "apple"), link_name = "__error")]
     #[cfg_attr(target_os = "haiku", link_name = "_errnop")]
     #[cfg_attr(target_os = "aix", link_name = "_Errno")]
+    #[cfg_attr(target_os = "qurt", link_name = "_Geterrno")]
     // SAFETY: this will always return the same pointer on a given thread.
     #[unsafe(ffi_const)]
     pub safe fn errno_location() -> *mut c_int;

library/std/src/sys/process/mod.rs

@@ -27,7 +27,7 @@ cfg_select! {
 mod env;
 
 pub use env::CommandEnvs;
-#[cfg(target_family = "unix")]
+#[cfg(all(target_family = "unix", not(target_os = "qurt")))]
 pub use imp::getppid;
 pub use imp::{
     ChildPipe, Command, CommandArgs, EnvKey, ExitCode, ExitStatus, ExitStatusError, Process, Stdio,

library/std/src/sys/stdio/mod.rs

@@ -2,7 +2,7 @@
 
 cfg_select! {
     any(
-        all(target_family = "unix", not(target_os = "qurt")),
+        target_family = "unix",
         target_os = "hermit",
         target_os = "wasi"
     ) => {