[libc-commits] [libc] [libc] Migrate to using LIBC_NAMESPACE_DECL for namespace declaration (PR #98075)

[Joseph Huber via libc-commits]

jhuber6 wrote:

So, this replaces every single namespace declaration with the following?
```c
#define LIBC_NAMESPACE_DECL [[gnu::visibility("hidden")]] LIBC_NAMESPACE
```

Before that we need to identify all the entrypoints and make sure they retain default visibility. @frobtech suggested that we split that up into introducing a macro for exporting global variables, then we'd need to make sure that `LIBC_FUNCTION_ATTRS` includes default visibility.

However, that's if we want non-hidden visibility at all. The main effect of everything being hidden is that if someone does `clang -shared foo.c -lc` with our `libc` the symbols won't be visible from the shared library. Maybe that's the desired behavior? The GPU doesn't care because we have no shared libraries.

https://github.com/llvm/llvm-project/pull/98075