[flang] [llvm] [flang-rt] Add experimental support for GPU build (PR #131826)

[Joseph Huber via llvm-commits]

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@@ -88,6 +87,54 @@ set(host_sources
   unit-map.cpp
 )
 
+# Sources that can be compiled directly for the GPU.
+set(gpu_sources
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jhuber6 wrote:

Mostly this is just the list of files that didn't error. There's a few different ones from the existing offloading builds, mostly due to the fact that we don't borrow the system's headers. I was thinking of a creative way to split these up but figured this was easiest.

Most of these fail due to missing headers, mostly POSIX related things because as much as we try `pthreads` and `sema` are not going to work on a GPU.

https://github.com/llvm/llvm-project/pull/131826