Process: unwrap the posix_spawnattr_t on Android (#5185)

This is required as while `posix_spawnattr_init` permits a nullable
type, `posix_spawnattr_setflags` properly expects a non-null parameter.
Unwrap the newly minted spawnattr or abort if the allocation failed.

Cherry pick commit #5179

Author: hjyamauchi

Sources/Foundation/Process.swift

@@ -944,6 +944,12 @@ open class Process: NSObject, @unchecked Sendable {
         var spawnAttrs: posix_spawnattr_t = posix_spawnattr_t()
 #endif
         try _throwIfPosixError(posix_spawnattr_init(&spawnAttrs))
+#if os(Android)
+        guard var spawnAttrs else {
+            throw NSError(domain: NSPOSIXErrorDomain, code: Int(errno),
+                          userInfo: [NSURLErrorKey:self.executableURL!])
+        }
+#endif
         try _throwIfPosixError(posix_spawnattr_setflags(&spawnAttrs, .init(POSIX_SPAWN_SETPGROUP)))
 #if canImport(Darwin)
         try _throwIfPosixError(posix_spawnattr_setflags(&spawnAttrs, .init(POSIX_SPAWN_CLOEXEC_DEFAULT)))