Previously this would just repeatedly overwrite the one file, which
makes it difficult to see what's happening when you compile a pipeline
that needs 3 routines.

Change-Id: Ibab115f5ccbb17333d504e4e7948be54ca304f9d
Bug: b/123193054
Reviewed-on: https://swiftshader-review.googlesource.com/c/23469Reviewed-by: Alexis Hétu <sugoi@google.com>
Tested-by: Chris Forbes <chrisforbes@google.com>