Fix embedded (arm-none-eabi) builds

Due to OS#3360, build testing for arm-none-eabi was unfortunately
skipped for a long time.  This is a number of fixes that make the
compile test pass again.

Related: OS#3360
Change-Id: I88e3c8e1a8786ca2a6a023b0d27c74be200a8588
diff --git a/src/logging.c b/src/logging.c
index 147b1fb..1dfd484 100644
--- a/src/logging.c
+++ b/src/logging.c
@@ -356,6 +356,7 @@
 	}
 	if (!cont) {
 		if (target->print_ext_timestamp) {
+#ifdef HAVE_LOCALTIME_R
 			struct tm tm;
 			struct timeval tv;
 			osmo_gettimeofday(&tv, NULL);
@@ -367,6 +368,7 @@
 			if (ret < 0)
 				goto err;
 			OSMO_SNPRINTF_RET(ret, rem, offset, len);
+#endif
 		} else if (target->print_timestamp) {
 			char *timestr;
 			time_t tm;