SwiftInspectLinux: re-order initialization

It seems that a recent change to the compiler will now optimize the
initializer and then the SIL verifier will fail due to the unintialized
member when the initializer is throwing and will never return without
initializing the member unless the initialization fails.

Author: compnerd

tools/swift-inspect/Sources/SwiftInspectLinux/PTrace.swift

@@ -33,24 +33,25 @@ public struct PTrace: ~Copyable {
   // process by calling cont().
   // NOTE: clients must use withPTracedProcess instead of direct initialization.
   fileprivate init(_ pid: pid_t) throws {
-    guard ptrace_attach(pid) != -1 else {
-      throw PTraceError.operationFailure(PTRACE_ATTACH, pid: pid)
+    self.pid = pid
+
+    guard ptrace_attach(self.pid) != -1 else {
+      throw PTraceError.operationFailure(PTRACE_ATTACH, pid: self.pid)
     }
 
     while true {
       var status: CInt = 0
-      let result = waitpid(pid, &status, 0)
+      let result = waitpid(self.pid, &status, 0)
       if result == -1 {
         if get_errno() == EINTR { continue }
-        throw PTraceError.waitFailure(pid: pid)
+        throw PTraceError.waitFailure(pid: self.pid)
       }
 
-      precondition(pid == result, "waitpid returned unexpected value \(result)")
+      precondition(self.pid == result,
+                   "waitpid returned unexpected value \(result)")
 
       if wIfStopped(status) { break }
     }
-
-    self.pid = pid
   }
 
   deinit { _ = ptrace_detach(self.pid) }