Otherwise, systems that don't support it will treat it as a name for a
global `struct ntp_msg` variable.

This partially reverts commit a7577667d6.
The musl C library does not use an internal cdefs.h header. As a result,
the definitions in sys/cdefs.h have no effect. This breads the build as
follows:
In file included from adjfreq_linux.c:23:0:
../src/ntpd.h:448:8: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘void’
__dead void fatal(const char *, ...)
^~~~
../src/ntpd.h:450:8: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘void’
__dead void fatalx(const char *, ...)
^~~~
Refer the related musl FAQ about cdefs.h:
http://wiki.musl-libc.org/wiki/FAQ#Q:_I.27m_trying_to_compile_something_against_musl_and_I_get_error_messages_about_sys.2Fcdefs.h
Keep the compiler attribute definition.
Remove also from noinst_HEADERS.

Solaris and illumos based distributions) which don't have it.

e0ed8ed664 went too far and broke the
backward compat headers for Linux systems.

This also removes the need for __weak_alias shims

do not have it, and a getifaddrs substitute for Solaris 10.

There are crypto hash function symbol overlaps between libmd and libcrypto on
FreeBSD, which causes hashing of the certificates store to fail as a
side-effect when using TLS constraints. Since all we really need is MD5, just
use the embedded OpenBSD versions instead.

I could not find a lot of precedence for this, because most time
daemons do not actually look at the value of olddelta. Account for
olddelta getting stuck at 1ms, and for a NULL value of delta being
treated as an error condition.

- add closefrom fallback for OS X / Linux systems, extracted from sudo,
but without the optimized versions, since they cannot work in a
chroot environment (and we're not performance critical here.)
- enable detecting libtls
- conditionally enable https constraint support

Due to some circular dependencies on Solaris, this needs to be defined
as a macro. We should just remove SA_LEN usage here next.

Handle 'NULL', emit the program name.

reported by Loganaden Velvindron

Call the compat code and select the correct emulation mode.
Remove the string encoding support, since we have fixed inputs for the
title string.

If sa_family is not set, sa_len should be zero.

I removed all of the code in fake-sensors, I don't think Henning wants
all the credit for an empty file.

TODO: convert u_int_* types to uint_*

Well, support may be too concrete of a term. There is a lot that is
missing in OS X, and not everything can be implemented with portability
shims. The time APIs in OS X seem to have frozen with NeXTSTEP and never
advanced with POSIX.

Remove dependency on libcrypto, include hash headers in a nicer way.

First attempt at building a new OpenNTPD portable project, based on the
latest OpenBSD source.