file(GENERATE): Create output file structures even earlier
Since commit b80557c7 we create the
cmSourceFile
instances marked with a GENERATED
source file property
before tracing source dependencies. Move it to even earlier so that
steps in cmGlobalGenerator::AddAutomaticSources
can operate on all
sources. This also avoids the accidental O(n^2)
calls for n
local
generators that we had previously.
This is also needed since !3884 (merged) to support file(GENERATE)
outputs as sources in a target with UNITY_BUILD
enabled.