Arch_DebuggerIsAttachedPosix failure

[marsupial]

Description of Issue

Arch_DebuggerIsAttachedPosix can return true in cases where the process is in fact not being debugged (on OS X always and on Linux when YAMA trace_scope is enabled). This will hang after a crash as it assumes the process is being traced. Fixed on OS X by testing if debugger is attached according to Apple docs, and on Linux by making sure the forked child has permission to attach.

Steps to Reproduce

1. Run testTfSIGSEGV SIGSEGV on OS X or Ubuntu Trusty. Or call Arch_DebuggerIsAttachedPosix on either platform and it will always return true.

System Information (OS, Hardware)

OS X & Ubuntu Linux.

Pull requests #148 fixes this.

[jtran56]

Filed as internal issue #141902.

[marsupial]

For what its worth, the pull request was tied to incorrect commits to fix this issue.
That has been corrected.