[Pkg-cmake-team] Bug#1102350: cmake 4.0 couldn't find correct std module source file

[Leen Hawk]

Package: cmake
Version: 4.0.0

With these test file:

`CMakeLists.txt`:
```cmake
cmake_minimum_required(VERSION 4.0.0)
set(CMAKE_CXX_STANDARD 23)
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD "a9e1cf81-9932-4810-974b-6eccaf14e457")

set(CMAKE_CXX_STANDARD_REQUIRED OFF)
set(CMAKE_CXX_MODULE_STD 1)

project(cpptest VERSION 0.1.0 LANGUAGES CXX)

add_executable(cpptest main.cpp)
```
`main.cpp`:
```cpp
import std;
int main(){
      std::println("Hello world!");
}
```

It shows:
```shell
CMake Error at build/CMakeFiles/4.0.0/CMakeCXXCompiler.cmake:103 (target_sources):
   Cannot find source file:

     /usr/lib/gcc/x86_64-linux-gnu/include/c++/15/bits/std.cc
Call Stack (most recent call first):
   /usr/share/cmake-4.0/Modules/CMakeTestCXXCompiler.cmake:91 (include)
   CMakeLists.txt:8 (project)


CMake Error in CMakeLists.txt:
   No SOURCES given to target: __CMAKE__CXX23 at synth_2e5b435a2e6c


CMake Generate step failed.  Build files cannot be regenerated correctly.
```

I have change the `CMakeCXXCompiler.cmake`:
```
target_sources(__CMAKE::CXX23
   INTERFACE
   FILE_SET std TYPE CXX_MODULES
     BASE_DIRS  "/usr/lib/gcc/x86_64-linux-gnu/15/../include/c++/15/bits"
     FILES  "/usr/lib/gcc/x86_64-linux-gnu/15/../include/c++/15/bits/std.cc" "/usr/lib/gcc/x86_64-linux-gnu/15/../include/c++/15/bits/std.compat.cc")
endif ()
```
to
```
target_sources(__CMAKE::CXX23
   INTERFACE
   FILE_SET std TYPE CXX_MODULES
     BASE_DIRS  "/usr/include/c++/15/bits"
     FILES  "/usr/include/c++/15/bits/std.cc" "/usr/include/c++/15/bits/std.compat.cc")
endif ()
```
to fix it. And there is my issue on kitware cmake:https://gitlab.kitware.com/cmake/cmake/-/issues/26609

They have fixed in gentoo and fedora. But debian doesn't.
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