<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/88433>88433</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libc] Add proxy header `hdr/float-macros.h`
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            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 

Similar PR: https://github.com/llvm/llvm-project/pull/87598, https://github.com/llvm/llvm-project/issues/87863.

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

- [ ] Add `libc/hdr/float_macros.h` that will include the system <float.h> in overlay mode or include `libc/include/llvm-libc-macros/float-macros.h` in full build mode.
- [ ] Add its corresponding cmake targets in `libc/hdr/CMakeLists.txt`.
- [ ] Remove the `#include_next <float.h>` in `libc/include/llvm-libc-macros/float-macros.h` and all the diagnostic suppression around it.
- [ ] Move the *filling-in* parts such as
```
#ifndef FLT_RADIX
#define FLT_RADIX __FLT_RADIX__
#endif // FLT_RADIX
```
to the proxy header `libc/hdr/float_macros.h` in the overlay mode, after including the system `<float.h>`.
- [ ] Change macro definitions in the full build header `libc/include/llvm-libc-macros/float-macros.h` to something like:
```
#ifdef __FLT_RADIX__
#define FLT_RADIX __FLT_RADIX__
#else
#define FLT_RADIX 2
#endif // FLT_RADIX
```
- [ ] Add their corresponding bazel targets in utils/bazel/llvm-project-overlay/libc/BUILD.bazel.
- [ ] Update bazel dependencies.
- [ ] Test in overlay mode:
```
from "llvm-project/build":
$ cmake ../llvm -GNinja -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS=libc
$ ninja libc
$ ninja check-libc
```
- [ ] Test in full build mode:
```
from "llvm-project/build":
$ cmake ../llvm -GNinja -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS="llvm;clang;compiler-rt;libc" -DLLVM_LIBC_INCLUDE_SCUDO=ON -DLLVM_LIBC_FULL_BUILD=ON
$ ninja libc
$ ninja check-libc
```
- [ ] Test bazel build:
```
from "llvm-project/utils/bazel/"
$ bazel clean
$ bazel build --config=generic_clang --features=layering_check @llvm-project//libc/...
$ bazel test --config=generic_clang --features=layering_check @llvm-project//libc/...
```
</pre>
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