Don't set a software stepping breakpoint at 0 on arm or mips.

Summary:
Check whether the setting the breakpoint failed during instruction emulation. If
it did, the next pc is likely in unmapped memory, and the inferior will crash
anyway after the next instruction. Do not return an error in this case, but just
continue stepping.
Reenabled the crash during step test for android/linux.

Reviewers: labath

Subscribers: aemerson, rengolin, tberghammer, danalbert, srhines, lldb-commits

Differential Revision: https://reviews.llvm.org/D25926
Author: Jason Majors <jmajors@google.com>

llvm-svn: 285187