Fix '[clang-tidy] use of undeclared identifier 'str' [clang-diagnostic-error]' issue in clang.c

[SoftaCheck](https://softacheck.com/app/repository/SoftaCheck/test-repo-cpp/issues?ignore=0&page=1) found an issue: [clang-tidy] use of undeclared identifier 'str' [clang-diagnostic-error] It's currently on: [clang.c](https://softacheck.com/app/repository/SoftaCheck/test-repo-cpp/issues?ignore=0&page=1)