3c64a98180
Summary: The `errno` variable is expected to be `thread_local` by the standard. However, the GPU targets do not support `thread_local` and implementing that would be a large endeavor. Because of that, we previously didn't provide the `errno` symbol at all. However, to build some programs we at least need to be able to link against `errno`. Many things that would normally set `errno` completely ignore it currently (i.e. stdio) but some programs still need to be able to link against correct C programs. For this purpose this patch exports the `errno` symbol as a simple global. Internally, this will be updated atomically so it's at least not racy. Externally, this will be on the user. I've updated the documentation to state as such. This is required to get `libc++` to build.
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