Include paths specified with -iquote are not considered in the C++ code model

When using quoted include paths like #include "a/b.h" in combination with the compiler flag -iquote a the include path is ignored by the C++ code model of QTCreator. I think this is the problematic code place where -iquote is missing. -iquote is a valid command line argument for Clang: https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-iquote-directory

This is a minimal reproducer:
 

$ mkdir -p /home/user/bug/a
$ touch /home/user/bug/a/b.h
$ mkdir -p /home/user/bug/c
$ cat /home/user/bug/c/main.cpp
#include "a/b.h"
int main()
{
    return 0;
}
$ cat /home/user/bug/compile_commands.json
[
{"command":"/usr/bin/gcc -iquote /home/user/bug -c main.cpp","directory":"/home/user/bug/c","file":"main.cpp"}
]

After loading the project in the editor a "file not found" error is reported by the code model.

Replacing -iquote in the compile_commands.json with -I or -isystem makes the code model valid. Using "Inspect C++ CodeModel..."  reveals that with -iquote the path is missing and when using -I or -isystem the path is added as a type UserPath.