Bug 506320

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SUMMARY
I use ccls as language server, and it will make KDEClangFormat unhappy when I run cmake.

STEPS TO REPRODUCE
0. Have clang-format executable
1. Have ccls run as your language server in the kwin repo
2. cmake in the kwin repo
3. 

OBSERVED RESULT
CMake Error at /home/user/kde/usr/share/ECM/kde-modules/KDEClangFormat.cmake:97 (add_custom_target):
  The target name
  "clang-format-.ccls-cache_@@home@user@kde@src@kwin_@usr@include@gentoo@fortify.h"
  is reserved or not valid for certain CMake features, such as generator
  expressions, and may result in undefined behavior.
Call Stack (most recent call first):
  CMakeLists.txt:517 (kde_clang_format)


CMake Error at /home/user/kde/usr/share/ECM/kde-modules/KDEClangFormat.cmake:100 (add_custom_command):
  No TARGET
  'clang-format-.ccls-cache_@@home@user@kde@src@kwin_@usr@include@gentoo@fortify.h'
  has been created in this directory.
Call Stack (most recent call first):
  CMakeLists.txt:517 (kde_clang_format)

(and more errors like this)

EXPECTED RESULT
No errors should occur.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: irrelevant
KDE Plasma Version: irrelevant
KDE Frameworks Version: master (from kdesrc-build)
Qt Version: irrelevant

ADDITIONAL INFORMATION
The KDEClangFormat.cmake says the following:
```
To exclude directories from the formatting add a ``.clang-format``
file in the directory with the following contents:

.. code-block:: yaml

   DisableFormat: true
   SortIncludes: false
```

But after I added .clang-format file with the specified content inside .ccls-cache and it still show up the errors in cmake.

contents in the .ccls-cache directory:
```
] find ~/kde/src/kwin/.ccls-cache
/home/user/kde/src/kwin/.ccls-cache
/home/user/kde/src/kwin/.ccls-cache/.clang-format
/home/user/kde/src/kwin/.ccls-cache/@home@user@kde@src@kwin
/home/user/kde/src/kwin/.ccls-cache/@home@user@kde@src@kwin/src@plugins@kdecorations@aurorae@src@aurorae.h.blob
/home/user/kde/src/kwin/.ccls-cache/@home@user@kde@src@kwin/src@plugins@kdecorations@aurorae@src@aurorae.cpp.blob
/home/user/kde/src/kwin/.ccls-cache/@home@user@kde@src@kwin/src@plugins@kdecorations@aurorae@src@config@auroraeconfig.h
/home/user/kde/src/kwin/.ccls-cache/@home@user@kde@src@kwin/src@plugins@kdecorations@aurorae@src@auroraeshared.h
/home/user/kde/src/kwin/.ccls-cache/@home@user@kde@src@kwin/src@plugins@kdecorations@aurorae@src@decorationoptions.h
/home/user/kde/src/kwin/.ccls-cache/@home@user@kde@src@kwin/src@plugins@kdecorations@aurorae@src@config@auroraeconfig.cpp.blob
/home/user/kde/src/kwin/.ccls-cache/@home@user@kde@src@kwin/src@plugins@kdecorations@aurorae@src@decorationoptions.h.blob
/home/user/kde/src/kwin/.ccls-cache/@home@user@kde@src@kwin/src@plugins@kdecorations@aurorae@src@aurorae.cpp
/home/user/kde/src/kwin/.ccls-cache/@home@user@kde@src@kwin/src@plugins@kdecorations@aurorae@src@auroraeshared.h.blob
/home/user/kde/src/kwin/.ccls-cache/@home@user@kde@src@kwin/src@plugins@kdecorations@aurorae@src@lib@themeconfig.h
/home/user/kde/src/kwin/.ccls-cache/@home@user@kde@src@kwin/src@plugins@kdecorations@aurorae@src@aurorae.h
/home/user/kde/src/kwin/.ccls-cache/@home@user@kde@src@kwin/src@plugins@kdecorations@aurorae@src@lib@themeconfig.h.blob
/home/user/kde/src/kwin/.ccls-cache/@home@user@kde@src@kwin/src@plugins@kdecorations@aurorae@src@config@auroraeconfig.h.blob
/home/user/kde/src/kwin/.ccls-cache/@home@user@kde@src@kwin/src@plugins@kdecorations@aurorae@src@config@auroraeconfig.cpp
/home/user/kde/src/kwin/.ccls-cache/@@home@user@kde@src@kwin
/home/user/kde/src/kwin/.ccls-cache/@@home@user@kde@src@kwin/@usr@include@gentoo@fortify.h.blob
/home/user/kde/src/kwin/.ccls-cache/@@home@user@kde@src@kwin/@usr@include@gentoo@maybe-stddefs.h.blob
/home/user/kde/src/kwin/.ccls-cache/@@home@user@kde@src@kwin/@usr@include@gentoo@fortify.h
/home/user/kde/src/kwin/.ccls-cache/@@home@user@kde@src@kwin/@usr@include@stdc-predef.h
/home/user/kde/src/kwin/.ccls-cache/@@home@user@kde@src@kwin/@usr@include@gentoo@maybe-stddefs.h
/home/user/kde/src/kwin/.ccls-cache/@@home@user@kde@src@kwin/@usr@include@stdc-predef.h.blob
```