[clang] [clang][ssaf] Fix CLANG_PLUGIN_SUPPORT=OFF SSAFExamplePlugin cmake errors (PR #191229)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-gcc-ubuntu` running on `sie-linux-worker3` while building `clang` at step 4 "cmake-configure".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/174/builds/34291

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 4 (cmake-configure) failure: cmake (failure)
...

    "/opt/ccache/bin/gcc"

  is not able to compile a simple test program.

  It fails with the following output:

    Change Dir: /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/CMakeFiles/CMakeScratch/TryCompile-JTM5xs
    
    Run Build Command(s):/usr/bin/ninja cmTC_8b03c && [1/2] Building C object CMakeFiles/cmTC_8b03c.dir/testCCompiler.c.o
    FAILED: CMakeFiles/cmTC_8b03c.dir/testCCompiler.c.o 
    /opt/ccache/bin/gcc    -o CMakeFiles/cmTC_8b03c.dir/testCCompiler.c.o -c /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/CMakeFiles/CMakeScratch/TryCompile-JTM5xs/testCCompiler.c
    ccache: error: Failed to create directory /home/buildbot/.ccache/tmp: No such file or directory
    ninja: build stopped: subcommand failed.
    
    

  

  CMake will not be able to correctly generate this project.
Call Stack (most recent call first):
  CMakeLists.txt:70 (project)


-- Configuring incomplete, errors occurred!
See also "/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/CMakeFiles/CMakeOutput.log".
See also "/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/CMakeFiles/CMakeError.log".

```

</details>

https://github.com/llvm/llvm-project/pull/191229