Wysiwyg strings are a D feature, not C11.
@ibuclaw created dlang/dmd pull request #13775 "fix Issue 22852 - importC: Lexer allows invalid wysiwyg and hex strings" fixing this issue: - fix Issue 22852 - importC: Lexer allows invalid wysiwyg and hex strings https://github.com/dlang/dmd/pull/13775
dlang/dmd pull request #13775 "fix Issue 22852 - importC: Lexer allows invalid wysiwyg and hex strings" was merged into stable: - ab286c2474c47d93aabaaac23dd4b37fffad0f36 by Iain Buclaw: fix Issue 22852 - importC: Lexer allows invalid wysiwyg and hex strings https://github.com/dlang/dmd/pull/13775
dlang/dmd pull request #13785 "merge stable" was merged into master: - 21c1aeff52e1f835b3e4a7a2946cf1d1dba455bd by Iain Buclaw: fix Issue 22852 - importC: Lexer allows invalid wysiwyg and hex strings https://github.com/dlang/dmd/pull/13785