runtime: let ARM32 EABI personality function continue unwind when called from traceback

runtime: let ARM32 EABI personality function continue unwind when called from traceback

    On ARM32 EABI, unlike other platforms, the personality function is
    called during _Unwind_Backtrace (libgcc/unwind-arm-common.inc:581).
    In this case, simply unwind the frame without returning any
    handlers. Otherwise traceback will loop if there is a frame with
    a defer on stack.

    Reviewed-on: https://go-review.googlesource.com/c/155759

From-SVN: r267434