MFC r256030:

Pull in r189644 from upstream llvm trunk:

  Add ms_abi and sysv_abi attribute handling.

  Based on a patch by Benno Rice!

This will help to develop EFI support.

Verified by:	benno
MFC r255931:

Fix a bug in ld, where indirect symbols are not handled properly during
linking of a shared library, leading to corrupt indexes in the dynamic
symbol table.  This should fix the multimedia/ffmpegthumbnailer port.

Reported by:	swills