includ cuda/cuda.jl during precompile, even if cuda isn't detected

src/Flux.jl

@@ -39,24 +39,14 @@ include("data/Data.jl")
 
 include("deprecations.jl")
 
-function __init__()
-  precompiling = ccall(:jl_generating_output, Cint, ()) != 0
-
-  # we don't want to include the CUDA module when precompiling,
-  # or we could end up replacing it at run time (triggering a warning)
-  precompiling && return
-
-  if !CuArrays.functional()
-    # nothing to do here, and either CuArrays or one of its dependencies will have warned
-  else
-    use_cuda[] = true
-
-    # FIXME: this functionality should be conditional at run time by checking `use_cuda`
-    #        (or even better, get moved to CuArrays.jl as much as possible)
-    if CuArrays.has_cudnn()
 include(joinpath(@__DIR__, "cuda/cuda.jl"))
-    else
-      @warn "CuArrays.jl did not find libcudnn. Some functionality will not be available."
+
+
+function __init__()
+  use_cuda[] = CuArrays.functional() # Can be overridden after load with Flux.use_cuda[] = false
+  if CuArrays.functional()
+    if !CuArrays.has_cudnn()
+      @warn "CuArrays.jl found cuda, but did not find libcudnn. Some functionality will not be available."
     end
   end
 end