[LynxOS] Include sys/ptrace.h instead of ptrace.h.

[LynxOS] Include sys/ptrace.h instead of ptrace.h.

This is one of the changes needed in order to build gdbserver on
LynxOS 5.x.

Really interesting: On LynxOS 4.x, there is a #warning when sys/ptrace.h
is used (explaining that ptrace.h will be used instead), whereas this
file was removed from LynxOS 5.x. The contents of sys/ptrace.h on 4.x
(or at least the meat of it):

    #if defined(__GNUC__) || defined(__GNUG__)
    #if !defined(__NO_INCLUDE_WARN__)
    #warning Using <ptrace.h> instead of <sys/ptrace.h>
    #endif /* defined(__NO_INCLUDE_WARN__) */
    #endif /* defined(__GNUC__) || defined(__GNUG__) */

    #include <ptrace.h>

The fix I went for, for now, is to just include <sys/ptrace.h>
unconditionally.  I could have done some configury, but we already
have to build with -D__NO_INCLUDE_WARN__ to avoid the warnings
anyway, and that's unvoidable, due to system includes themselves
including the "wrong" header file.

Since <sys/ptrace.h> seems to be the choice that was made for LynxOS,
and since it works to include it on LynxOS 4.x, I think that's the simplest
solution.

gdb/gdbserver/ChangeLog:

        * lynx-low.c, lynx-ppc-low.c: Include <sys/ptrace.h> instead of
        <ptrace.h>