[Process] Warn user with a useful message when tmpfile() failed
[Process] Fix regression introduced in #6620 / 880da01c49a9255f5022ab7e18bca38c18f56370, fixes #7082
Merge branch '2.0' into 2.1

* 2.0:
  [Process] Fix regression introduced in #6620 / 880da01c49a9255f5022ab7e18bca38c18f56370, fixes #7082