Add an unnamed pipe fail-safe to launching lldb-gdbserver.

Summary:
Currently, launching lldb-gdbserver from platform on Android requires root for
mkfifo() and an explicit TMPDIR variable. This should remove both requirements.

Test Plan: Successfully launched lldb-gdbserver on a non-rooted Android device.

Reviewers: tberghammer, vharron, clayborg

Reviewed By: clayborg

Subscribers: tberghammer, lldb-commits

Differential Revision: http://reviews.llvm.org/D9307

llvm-svn: 235940