[clang] [Clang] Fix crash when building a module with CC_PRINT_HEADERS_FORMAT=json (PR #136227)

[Bob Wilson via cfe-commits]

bob-wilson wrote:

I'm still investigating what to do for modules. It's not yet clear if that should be handled along with `CC_PRINT_HEADERS_FORMAT=json` or some new option. I figured it would be good to start by fixing the crashes.

https://github.com/llvm/llvm-project/pull/136227