Fix handling of D_GIANTOK

It was meant to suppress only the printf(), not the subsequent injection
of Giant-protected thunks for various file operations.

Fixes: fbeb4ccac9
Reported by: pho
Tested by: pho
Pointy hat: markj

(cherry picked from commit 887c753c9f451322cae3efbf9b63f53f3d9011c8)