[ELF] - Teach LLD to recognize PT_OPENBSD_BOOTDATA

Minor patch to fix PR31288

OpenBSD commit:
https://github.com/openbsd/src/commit/d39116912b9536bd77326260dc5c6e593fd4ee24

Differential revision: https://reviews.llvm.org/D27458

llvm-svn: 288832