Help adapting anything like "techpack/camera" for successful building using gcc 6 (PostmarketOS), if any error came up, that not script fault, that means OEM provide not so good sources, but it will be easy to fix. Usage: python3 AbsoluteToRelative.py "PATH where to replace all includes to relative one". THAT SCRIPT ALSO GOES IN SUBDIRECTORIES!!!

AbsoluteToRelative.py

import os
import subprocess
import sys

def find(name, path):
    for root, dirs, files in os.walk(path):
        if name in files:
            return os.path.join(root, name)

arr = []
for root, dirs, files in os.walk(sys.argv[1]):
    path = root.split(os.sep)
    for file in files:
        with open(root + os.sep + file, "r") as f:
            arr = f.readlines()
        for i in range(0,len(arr)):
            line = arr[i]
            # find include lines and check if already relative
            if(('#include "' in line and '.h"' in line) and "/" not in line):
                toreplaceline = line.split('#include "')[1].split('"')[0]
            elif(('#include <' in line and '.h>' in line) and "/" not in line):
                toreplaceline = line.split('#include <')[1].split('>')[0]
            else:
                continue
            #find file to be replaced(need no same names in any subdirectories to work properly)
            toreplace = find(toreplaceline, sys.argv[1])
            #find relative path
            try:
                rel = os.path.relpath(toreplace,root + os.sep + file).replace("../", "", 1)
                #check if it for some reason including himself
                if(rel == "."): rel = file
            except:
                continue
            arr[i] = '#include "' + rel + '"\n'
            with open(root + os.sep + file,'w') as f: 
                f.writelines(arr) 
                f.close()