[ELF][ARM] Accept and ignore -p and -no-pipleline-knowledge

The linux kernel uses an old flag -p/-no-pipeline-knowledge that is
accepted by bfd and gold but ignored by modern versions of them. The
original option is very old and is pre-ABI, it sometimes comes up in
code-bases that had support for pre ABI toolchains. The Linux kernel uses
it in 3 places in the ARM specific section.

Differential Revision: https://reviews.llvm.org/D58540

llvm-svn: 354769