logger: check for ntp_gettime() rather than for timex.h

It seems that musl libc and uClibc without UCLIBC_NTP_LEGACY
does not provide ntp_gettime and compile will fail.

References: https://github.com/karelzak/util-linux/issues/174
Signed-off-by: Karel Zak <kzak@redhat.com>
diff --git a/configure.ac b/configure.ac
index 3dcfb74..cedf761 100644
--- a/configure.ac
+++ b/configure.ac
@@ -343,6 +343,7 @@
 	lseek64 \
 	mempcpy \
 	nanosleep \
+	ntp_gettime \
 	open_memstream \
 	personality \
 	posix_fadvise \
diff --git a/misc-utils/logger.c b/misc-utils/logger.c
index 0a9e4ab..2fd3ddf 100644
--- a/misc-utils/logger.c
+++ b/misc-utils/logger.c
@@ -366,9 +366,6 @@
 {
 	char *hostname = NULL;
 	char pid[32], time[64], timeq[80];
-#ifdef HAVE_SYS_TIMEX_H
-	struct ntptimeval ntptv;
-#endif
 	struct timeval tv;
 	struct tm *tm;
 
@@ -408,7 +405,9 @@
 		snprintf(pid, sizeof(pid), " %d", ctl->pid);
 
 	if (ctl->rfc5424_tq) {
-#ifdef HAVE_SYS_TIMEX_H
+#ifdef HAVE_NTP_GETTIME
+		struct ntptimeval ntptv;
+
 		if (ntp_gettime(&ntptv) == TIME_OK)
 			snprintf(timeq, sizeof(timeq),
 				 " [timeQuality tzKnown=\"1\" isSynced=\"1\" syncAccuracy=\"%ld\"]",