[clang] [clang-format] Set C11 instead of C17 for LK_C (PR #134472)

[Owen Pan via cfe-commits]

owenca wrote:

> But why does this fix it?

See [here](https://github.com/llvm/llvm-project/blob/52eb11f925ddeba4e1b3840fd636ee87387f3ada/clang/lib/Lex/Lexer.cpp#L3893). Somehow I thought that setting C17 would also set C11. 😞 

https://github.com/llvm/llvm-project/pull/134472