[lldb] [MainLoop] Report errno for failed kevent()
[lldb] [MainLoop] Report errno for failed kevent()

Modify the kevent() error reporting to use errno rather than returning
the return value.  At least on FreeBSD and NetBSD, kevent() always
returns -1 in case of error, and the actual error is returned via errno.

Differential Revision: https://reviews.llvm.org/D58229

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@354029 91177308-0d34-0410-b5e6-96231b3b80d8

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