Support C compiler build

[ityuhui]

Because the upstream repo changes the compiler to C by OpenAPITools/openapi-generator#20289 , the build failed by default:

CMake Error at /usr/local/share/cmake-3.31/Modules/CheckSymbolExists.cmake:163 (try_compile):
  Unknown extension ".cxx" for file

    /home/runner/work/c/c/kubernetes/build/CMakeFiles/CMakeScratch/TryCompile-NwLhCQ/CheckSymbolExists.cxx

  try_compile() works only for enabled languages.  Currently these are:

    C

We can fix the build error by the following 2 solutions:

1. Add C++ support to CMakeList.txt

enable_language(CXX)

This change needs to be committed to the upstream repository. Otherwise it will be overwritten every time this client is regenerated.

2. Change the CheckCXXSymbolExists to CheckSymbolExists to support C compiler.

Now, I would recommend solution 2, since we can support C compiler to compile this project.

[brendandburns]

/lgtm
/approve

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