FreeBSD: attach to pid from different cwd
FreeBSD: attach to pid from different cwd

attach by pid worked when running from the directory from which the
target was launched, but failed from a different directory. Use the
kern.proc.pathname sysctl to locate the target, falling back to the
original case of the target's argv[0] if that fails. Based on a patch
from Vignesh Balu.

Differential Revision:	https://reviews.llvm.org/D32271


git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@312430 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb