elf-loader: avoid module self-referencing on local symbols resolution

Function object::resolve_pltgot() should never put "this" to
_used_by_resolve_plt_got collection. Otherwise module locks itself
in memory forever.

This problem makes native applications fail in different ways
on multiple consequtive executions because .bss sections are
not zeroed between main() invocations.

In particular iperf fails to parse command line arguments because its
corresponding code heavily relies on global variables.

Signed-off-by: Dmitry Fleytman <dmitry@daynix.com>
Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>
run-elf: cancel alarms after native program execution

Native program may leave alarm pending on exit,
cancel it before module unload.

Signed-off-by: Dmitry Fleytman <dmitry@daynix.com>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>
xen: comment out HYPERVISOR_poll()

Has a call to get_system_time(), which doesn't exist, so the link fails with
mode=debug.  Exposed by 98fc8c187cf76a1e ("build: Use -O0 for debug build
instead of -Og").

Signed-off-by: Avi Kivity <avi@cloudius-systems.com>