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

[Jan Svoboda via cfe-commits]

jansvoboda11 wrote:

Since this is trying to make `CC_PRINT_HEADERS_FORMAT` work for modules, I have to ask: should it report module map files too?

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