headers included with relative paths are not found

[firewave]

Encountered while working on #438.

#include <inc/inc.h>

a.cpp:1: missing header: Header not found: <inc/inc.h>

libstdc++ uses such includes.

[firewave]

My example was flawed. System include are only looked for in the provided include paths. The following works:

a.cpp

#include <bits/c++config.h>

./simplecpp a.cpp -I/usr/include/c++/15.1.1/x86_64-pc-linux-gnu

The files in question:

find /usr/include -name c++config.h
/usr/include/c++/15.1.1/x86_64-pc-linux-gnu/bits/c++config.h
/usr/include/c++/15.1.1/x86_64-pc-linux-gnu/32/bits/c++config.h`

I was seeing a failure in the CI because of a typo.