[llvm] [Offload] Fix missing dependencies in Offload API generation (PR #142776)

[Krzysztof Parzyszek via llvm-commits]

kparzysz wrote:

This happens when I start with an empty directory as the build tree.  Once it's populated with make files and subdirectories (with these two created by hand), everything works in all subsequent builds.

https://github.com/llvm/llvm-project/pull/142776