split out mlrdatetime from mlrutil to ease iterative windows port

c/lib/mlrdatetime.c

@@ -0,0 +1,33 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/time.h>
+#include <sys/stat.h>
+#include "lib/mlrdatetime.h"
+
+// ----------------------------------------------------------------
+// seconds since the epoch
+double get_systime() {
+	struct timeval tv = { .tv_sec = 0, .tv_usec = 0 };
+	(void)gettimeofday(&tv, NULL);
+	return (double)tv.tv_sec + (double)tv.tv_usec * 1e-6;
+}
+
+// ----------------------------------------------------------------
+// See the GNU timegm manpage -- this is what it does.
+time_t mlr_timegm(struct tm* ptm) {
+	time_t ret;
+	char* tz;
+
+	tz = getenv("TZ");
+	setenv("TZ", "GMT0", 1);
+	tzset();
+	ret = mktime(ptm);
+	if (tz) {
+		setenv("TZ", tz, 1);
+	} else {
+		unsetenv("TZ");
+	}
+	tzset();
+	return ret;
+}

c/lib/mlrdatetime.h

@@ -0,0 +1,14 @@
+#ifndef MLRDATETIME_H
+#define MLRDATETIME_H
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+double get_systime();
+
+// portable timegm replacement
+time_t mlr_timegm (struct tm *ptm);
+
+#endif // MLRDATETIME_H