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

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> > I wonder if there are other places where we assume that a `::` token only exists in C++.
> 
> I didn't find any other places.

There are other places, but I think they can be handled in follow-ups. For example:

https://godbolt.org/z/Wsdh9T3Pb is an example where we assume `::` has meaning outside of C++ and change behavior (https://github.com/llvm/llvm-project/blob/df4bb1f3106d39e5c6b767a28c0531efbbebc2d2/clang/lib/Parse/ParseDecl.cpp#L3317)

or

https://github.com/llvm/llvm-project/blob/b8eebf2704f2ebb6894fd952e4f15fdb62270606/clang/lib/Parse/ParseDecl.cpp#L2013

(etc)

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