[clang] [Clang] Fix infinite loop on '::' inside parens in C mode (PR #195377)

[Richard Smith via cfe-commits]

zygoloid wrote:

I wonder if there are other places where we assume that a `::` token only exists in C++. Might be worth looking through each reference to the token kind if no-one's done that yet.

https://github.com/llvm/llvm-project/pull/195377