<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/88187>88187</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libc] Add proxy headers for fenv.h types.
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            good first issue,
            libc
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          lntue
      </td>
    </tr>
</table>

<pre>
    Context: https://github.com/llvm/llvm-project/pull/87017 https://github.com/llvm/llvm-project/pull/87598

This is the continuation of https://github.com/llvm/llvm-project/issues/87863.

Add a proxy header for fenv.h types so that our implementations and tests will work nicely for both overlay and full build modes.

- [ ]  Add `libc/hdr/fenv_t.h` and `libc\hdr\fexcept_t` that will include the system <fenv.h> in overlay mode or include the corresponding header in `libc/include/llvm-libc-types/` in full build mode.
- [ ] Add its corresponding cmake targets in libc/hdr/CMakeLists.txt.
- [ ] Replacing the remaining `#include <fenv.h>` and cmake target dependency on `libc.include.fenv`.
- [ ] Add their corresponding bazel targets in `utils/bazel/llvm-project-overlay/libc/BUILD.bazel`.
- [ ] Update bazel dependencies.
</pre>
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