I'm trying to use IWYU on my project on Ubuntu 18.04. I installed pre-build LLVM/Clang 8 and built IWYU with it.

My project was built successfully LLVM/Clang 8 and I then run IWYU on compile database. I got next errors:

In file included from /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/cstring:42:
/usr/include/string.h:33:10: fatal error: 'stddef.h' file not found
#include <stddef.h>

stddef.h doesn't exist in /usr/include, but it installed with LLVM/Clang and IWYU could deduce location from compile command.

I'm not sure that this problem is with IWYU, it may be problem in Clang tooling.