The go_darwin_arm_exec script now tells lldb to move the working
directory into <bundle>/src/os on startup.
Change-Id: I0ada4969e9ea374f08c84ab736aab2097ac73dd8
Reviewed-on: https://go-review.googlesource.com/6369 Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>