cerbero: Keep RSP files when building on Windows

This helps debug build issues since you need to look at the contents
of RSP files to see the actual arguments list, and they're
automatically deleted by default.
3 jobs for keep-rspfiles in 51 minutes and 56 seconds (queued for 1 minute and 13 seconds)
Status Job ID Name Coverage
  Preparation
passed #63476
manifest

00:00:19

 
  Build
passed #63477
cerbero deps fedora x86_64

00:40:25

 
  Full Builds
passed #63478
build cerbero fedora x86_64

00:11:10