We need to write a new problem matcher based on msCompile which can handle relative path.
Also, even if gcc handles relative and absolute paths already, make -f or -C moves the base of the build somewhere else than ${workspaceFolder} and we actually need a new problem matcher based on gcc, that would read from a variable that the extension sets when detecting -f or -C.
Also, if a make invokes other make in various different folders, think if we can have a smart problem matcher that would always recognize the base folder for relative path analysis. Most probable we cannot support this scenario.