BUG #17365: Error: redefinition of 'stat' in win32_port.h when including postgres.h

The following bug has been logged on the website:

Bug reference:      17365
Logged by:          Mario Emmenlauer
Email address:      mario@emmenlauer.de
PostgreSQL version: 14.1
Operating system:   Windows 10 with Clang-Cl 13.0.0 over MSVC 19.5
Description:

I'm compiling postgres with Microsoft Visual Studio 19.5. This generally
works well, thanks!

Then I build a wrapper library that uses `postgres.h` in my code. My code is
built using the LLVM Clang-Cl compiler frontend version 13.0.0 over
Microsoft Visual Studio 19.5. Generally, the Clang-Cl compiler frontend
works very well. But since updating PostgreSQL from 13.x to the 14.1
release, I get an error:
```
FAILED: CMakeFiles/DatabaseHandler.dir/src/BDAPGResult.cc.obj 
C:\BDA\ci\LLVM-13.0.0\bin\clang-cl.exe   -TP -DDATABASEHANDLER_DEBUG -DEBUG
-DFMT_LOCALE -DHasZLIB -DNOMINMAX -DWIN32 -DWIN64 -D_DEBUG -D_DEBUG_
-D_ENABLE_EXTENDED_ALIGNED_STORAGE -D_UNICODE -D_WIN64
-IC:\data\ci-tmp\Debug\DatabaseHandler
-IC:\BDA\bld\XTJyb_7r\0\DatabaseHandler\include
-IC:\BDA\bld\XTJyb_7r\0\DatabaseHandler\src
-IC:\data\ci-dst\Debug\include\server\port\win32 -imsvc
C:\data\ci-dst\Debug\include -imsvc C:\data\ci-dst\Debug\include\server
-imsvc C:\data\ci-dst\Tools\ipp\include -imsvc
C:\data\ci-dst\Tools\daal\include -imsvc C:\data\ci-dst\Tools\include -imsvc
C:\data\ci-dst\Debug\include\QtCore -imsvc
C:\data\ci-dst\Debug\mkspecs\win32-msvc -imsvc
C:\data\ci-dst\Debug\include\eigen3 -imsvc
C:\data\ci-dst\Debug\include\ITK-5.2 -imsvc
C:\data\ci-dst\Debug\include\QtGui /std:c++20 /MDd /Z7 -march=haswell
-Werror=pessimizing-move -Werror=redundant-move -Werror=range-loop-construct
 -Werror=range-loop-construct       /D_ITERATOR_DEBUG_LEVEL=0
/DWINVER=0x0A00 /D_WIN32_WINNT=0x0A00 /DDEBUG     /D_CRT_SECURE_NO_DEPRECATE
/D_SILENCE_ALL_CXX17_DEPRECATION_WARNINGS  -Wextra -Werror=return-type
-Werror=uninitialized -Werror=unknown-pragmas -Werror=shadow -Werror=undef
-Werror=pointer-arith -DQT_DISABLE_DEPRECATED_BEFORE=0x050F00
-Werror=shift-count-overflow -Werror=string-plus-int
-Werror=nonportable-include-path -Werror=inconsistent-missing-override
-Werror=self-assign -Werror=self-assign-field -Werror=self-move
-Werror=braced-scalar-init -Werror=many-braces-around-scalar-init
-Werror=return-stack-address -Werror=delete-non-abstract-non-virtual-dtor
/W4  -Werror=return-stack-address
-Werror=delete-non-abstract-non-virtual-dtor    /DWIN32 /D_WINDOWS /GR /EHsc
/Zi /Ob0 /Od /RTC1 -MDd /Zc:__cplusplus -Zc:__cplusplus -permissive- -utf-8
-std:c++20 /showIncludes
/FoCMakeFiles\DatabaseHandler.dir\src\BDAPGResult.cc.obj
/FdDatabaseHandler.pdb -c --
C:\BDA\bld\XTJyb_7r\0\DatabaseHandler\src\BDAPGResult.cc
In file included from
C:\BDA\bld\XTJyb_7r\0\DatabaseHandler\src\BDAPGResult.cc:31:
In file included from C:\data\ci-dst\Debug\include\server\postgres.h:46:
In file included from C:\data\ci-dst\Debug\include\server/c.h:1362:
In file included from C:\data\ci-dst\Debug\include\server/port.h:26:
C:\data\ci-dst\Debug\include\server/port/win32_port.h(256,8): error:
redefinition of 'stat'
struct stat                                             /* This should match
struct __stat64 */
       ^
C:\Program Files (x86)\Windows
Kits\10\include\10.0.19041.0\ucrt\sys/stat.h(87,12): note: previous
definition is here
    struct stat
           ^
1 error generated.
```

I've recently also changed from c++17 to c++20, so maybe this can be
related? I keep the full compile command in above log in case there is
anything else dubious?
Any help would be greatly appreciated!

    Mario