Build fails

[Tony Hain]

In an effort to put ntpviz on a machine with gnuplot installed, I did a git
clone tonight, and the build failed. Looks like differences in some h files,
related to noreturn vs. __noreturn__

...
[ 60/101] Compiling ntpd/ntp_monitor.c
In file included from ../../ntpd/ntp_monitor.c:7:
In file included from ../../include/ntpd.h:11:
In file included from ../../include/ntp.h:28:
In file included from ../../include/ntp_lists.h:110:
In file included from ../../include/ntp_assert.h:75:
In file included from ../../../../../../local/include/isc/assertions.h:28:
../../../../../../local/include/isc/platform.h:342:9: warning:
'ISC_PLATFORM_NORETURN_POST' macro redefined
#define ISC_PLATFORM_NORETURN_POST __attribute__((noreturn))
        ^
../config.h:88:9: note: previous definition is here
#define ISC_PLATFORM_NORETURN_POST __attribute__((__noreturn__))
        ^
../../ntpd/ntp_monitor.c:132:2: warning: implicit declaration of function
'ISC_LIKELY' is invalid in C99 [-Wimplicit-function-declaration]
        NTP_ENSURE(punlinked == mon);
        ^
../../include/ntp_assert.h:96:24: note: expanded from macro 'NTP_ENSURE'
#define NTP_ENSURE(x)           ENSURE(x)
                                ^
../../include/ntp_assert.h:87:20: note: expanded from macro 'ENSURE'
#define ENSURE(x)               ALWAYS_ENSURE(x)
                                ^
../../include/ntp_assert.h:80:26: note: expanded from macro 'ALWAYS_ENSURE'

...