cmake: internal/stage: make sure the file name is always lower case
cmake: internal/stage: make sure the file name is always lower case

This can cause problems when the target name contains upper characters

aldebaran/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild