Revert "Do not call getpid wrapper after fork in tests"

This reverts commit 12fbabd27f.

It was only needed because of using raw `clone3` instead of `fork`, but
we only do that now when a pidfd is requested.

src/test/ui/command/command-pre-exec.rs

@@ -8,6 +8,8 @@
 // ignore-sgx no processes
 #![feature(process_exec, rustc_private)]
 
+extern crate libc;
+
 use std::env;
 use std::io::Error;
 use std::os::unix::process::CommandExt;
@@ -15,23 +17,6 @@ use std::process::Command;
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::Arc;
 
-#[cfg(not(target_os = "linux"))]
-fn getpid() -> u32 {
-    use std::process;
-    process::id()
-}
-
-/// We need to directly use the getpid syscall instead of using `process::id()`
-/// because the libc wrapper might return incorrect values after a process was
-/// forked.
-#[cfg(target_os = "linux")]
-fn getpid() -> u32 {
-    extern crate libc;
-    unsafe {
-        libc::syscall(libc::SYS_getpid) as _
-    }
-}
-
 fn main() {
     if let Some(arg) = env::args().nth(1) {
         match &arg[..] {
@@ -83,12 +68,14 @@ fn main() {
     };
     assert_eq!(output.raw_os_error(), Some(102));
 
-    let pid = getpid();
+    let pid = unsafe { libc::getpid() };
+    assert!(pid >= 0);
     let output = unsafe {
         Command::new(&me)
             .arg("empty")
             .pre_exec(move || {
-                let child = getpid();
+                let child = libc::getpid();
+                assert!(child >= 0);
                 assert!(pid != child);
                 Ok(())
             })

src/test/ui/process/process-panic-after-fork.rs

@@ -23,21 +23,6 @@ use std::sync::atomic::{AtomicU32, Ordering};
 
 use libc::c_int;
 
-#[cfg(not(target_os = "linux"))]
-fn getpid() -> u32 {
-    process::id()
-}
-
-/// We need to directly use the getpid syscall instead of using `process::id()`
-/// because the libc wrapper might return incorrect values after a process was
-/// forked.
-#[cfg(target_os = "linux")]
-fn getpid() -> u32 {
-    unsafe {
-        libc::syscall(libc::SYS_getpid) as _
-    }
-}
-
 /// This stunt allocator allows us to spot heap allocations in the child.
 struct PidChecking<A> {
     parent: A,
@@ -59,7 +44,7 @@ impl<A> PidChecking<A> {
     fn check(&self) {
         let require_pid = self.require_pid.load(Ordering::Acquire);
         if require_pid != 0 {
-            let actual_pid = getpid();
+            let actual_pid = process::id();
             if require_pid != actual_pid {
                 unsafe {
                     libc::raise(libc::SIGUSR1);