Merge 81888 from mainline.

Change the marker byte for stubs from 0xcd to 0xce (another form of
interrupt instruction, which shouldn't arise any other way).  0xcd is
also used by JITMemoryManager to initialize the buffer to garbage,
which means it could appear following a noreturn call even when
that is not a stub, confusing X86CompilationCallback2.  PR 4929.

llvm-svn: 81981