Treat inttypes.h as a built-in header

[markrowe]

Summary

It wraps a system header. This allows the system module map to declare a
module for it.

https://bugs.llvm.org/show_bug.cgi?id=51307

[markrowe]

@dexonsmith Ping?

[dexonsmith]

@bruno or @vsapsai, any chance one of you knows whether this is correct?

[vsapsai]

In general it is correct but there is no test case. I have a test case but it fails for other reasons. And I wasn't able to find time to address these "other reasons". I'll post my version of the test case soon.

clang/lib/Lex/ModuleMap.cpp

#include "clang/Basic/TokenKinds.def"
   return Name;
 }
 
 /// Determine whether the given file name is the name of a builtin
 /// header, supplied by Clang to replace, override, or augment existing system
 /// headers.
 bool ModuleMap::isBuiltinHeader(StringRef FileName) {
   return llvm::StringSwitch<bool>(FileName)
            .Case("float.h", true)
+           .Case("inttypes.h", true)
            .Case("iso646.h", true)
            .Case("limits.h", true)
            .Case("stdalign.h", true)
            .Case("stdarg.h", true)
            .Case("stdatomic.h", true)
            .Case("stdbool.h", true)
            .Case("stddef.h", true)
            .Case("stdint.h", true)