amd64-darwin-tdep.c: Remove #include "gdb_assert.h"

gdb_assert.h is already included from darwin-nat.h, so no need to
include it again...

gdb/ChangeLog:

        * amd64-darwin-tdep.c: Remove #include "gdb_assert.h".
darwin-nat.c: Do not use gdb_assert on system call outcomes.

There were many cases were we make a system call which could fail
due to reasons outside of the debugger control. We should handle
these situations a little more gracefully than triggering an
internal error.

gdb/ChangeLog:

        * darwin-nat.c (darwin_mourn_inferior): Replace call to
        gdb_assert by call to MACH_CHECK_ERROR.
        (darwin_attach_pid): Raise an error rather than a failed
        assertion when various system calls failed.  Report a warning
        instead of raising a failed assertion when PREV_NOT is not NULL
        after call to mach_port_request_notification.
        (darwin_ptrace_me): Raise an error rather than a failed
        assertion when read returns nonzero.
darwin-nat: Print all hex values with 0x prefix.

gdb/ChangeLog:

        * darwin-nat.c: Replace all "%x" instances in format strings
        into "0x%x" throughout.
darwin: warning resuming inferior after attach

This patch avoids a warning when resuming the execution of a program
that we attached to. For instance:

    (gdb) attach 29989
    (gdb) continue
    Continuing.
    warning: Mach error at "/[...]/darwin-nat.c:738" in function
             "darwin_resume_thread": (os/kern) failure (0x5)

The warning is relatively harmless, but worrisome for the average
user.  The warning comes from the fact that darwin_wait recorded
that the fake stop event corresponding to the suspend action was
caused by the main thread being suspended on a SIGTRAP. As a result
of this, when resuming the program's execution, we try to resume
the thread's execution as well.  This is where the issue occurs,
as the thread was not in fact suspended, thus triggering the warning.

gdb/ChangeLog:

        * darwin-nat.c (darwin_setup_fake_stop_event): New function.
        (darwin_attach): Adjust using darwin_setup_fake_stop_event.