By default LLD will generate position independent Thunks when the --pie or --shared option is used. Reference to absolute addresses is permitted in other cases. For some embedded systems position independent thunks are needed for code that executes before the MMU has been set up. The option --pic-veneer is used by ld.bfd to force position independent thunks.
The patch adds an option --pic-thunk with --pic-veneer as an alias to support this option. The --pic-veneer option is needed for the Linux kernel on Arm.
Fixes pr39886 (https://bugs.llvm.org/show_bug.cgi?id=39886)