Track -dynamic/-fPIC to avoid obscure linker errors

[simonmar]

Using the wrong combination of -dynamic and/or -fPIC can lead to obscure linker errors, see e.g. #3705. We should track whether an object file was compiled with -dynamic and -fPIC so that we can give better error messages before running the linker.

See also

#3712

Implement -dynamic-lib option

[duncan]

Doing this on a per-object file basis will require adding extra custom sections to the object files. This is something we want to do anyway so that we can add other info such as:

• .hi file content
• stack trace debug info

The ability to insert and read custom sections will have to be implemented separately on each of ELF, Mach-O and PE. It should be possible to have a consistent interface on each platform however.