Do not try non-dwarf local unwinds for x86.

The frame-chain unwind code in libunwind never really works and it
has a high probability of trying to access unmapped memory. When
doing a remote unwind, this will simply result in the unwind stopping.
When doing a local unwind, this can lead to crashes. Disable this
method for local unwinds.

Bug: 26807329

(cherry picked from commit 936e80b1)

Change-Id: I0032ffd833b0b9e8931defef31e2277e41186abc