Don't enforce ABI stack alignment rules on the sigtramp frame --
its stack frame is a constructed, fake thing that may not conform
correctly to these rules.  This fixes a problem where lldb couldn't
backtrace past an asynchronous signal handler (_sigtramp) frame on
a stack on Mac OS X.
<rdar://problem/15035673> 


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@198450 91177308-0d34-0410-b5e6-96231b3b80d8