introduce HAVE_TM_GMTOFF_IN_TM

Not all architectures have the tm.tm_gmtoff member.  This fixes cygwin
builds.

openbsc/configure.ac

@@ -83,6 +83,30 @@ if test "$enable_coverage" = "yes"; then
    AC_SUBST([COVERAGE_LDFLAGS])
 fi
 
+AC_DEFUN([CHECK_TM_INCLUDES_TM_GMTOFF], [
+  AC_CACHE_CHECK(
+    [whether struct tm has tm_gmtoff member],
+    osmo_cv_tm_includes_tm_gmtoff,
+    [AC_LINK_IFELSE([
+      AC_LANG_PROGRAM([
+        #include <time.h>
+      ], [
+        time_t t = time(NULL);
+        struct tm* lt = localtime(&t);
+        int off = lt->tm_gmtoff;
+      ])
+    ],
+    osmo_cv_tm_includes_tm_gmtoff=yes,
+    osmo_cv_tm_includes_tm_gmtoff=no
+    )]
+  )
+  if test "x$osmo_cv_tm_includes_tm_gmtoff" = xyes; then
+    AC_DEFINE(HAVE_TM_GMTOFF_IN_TM, 1,
+              [Define if struct tm has tm_gmtoff member.])
+  fi
+])
+
+CHECK_TM_INCLUDES_TM_GMTOFF
 
 dnl Generate the output
 AM_CONFIG_HEADER(bscconfig.h)

openbsc/src/libmsc/gsm_04_08.c

@@ -29,6 +29,8 @@
 #include <time.h>
 #include <netinet/in.h>
 
+#include "bscconfig.h"
+
 #include <openbsc/auth.h>
 #include <openbsc/db.h>
 #include <openbsc/debug.h>
@@ -734,7 +736,12 @@ int gsm48_tx_mm_info(struct gsm_subscriber_connection *conn)
 		/* Need to get GSM offset and convert into 15 min units */
 		/* This probably breaks if gmtoff returns a value not evenly divisible by 15? */
 		local_time = localtime(&cur_t);
+#ifdef HAVE_TM_GMTOFF_IN_TM
 		tzunits = (local_time->tm_gmtoff/60)/15;
+#else
+#warning find a portable way to obtain the timezone offset
+		tzunits = 0;
+#endif
 		if (tzunits < 0) {
 			tzunits = tzunits/-1;
 			ptr8[7] = bcdify(tzunits);

openbsc/src/libmsc/gsm_04_11.c

@@ -32,6 +32,8 @@
 #include <time.h>
 #include <netinet/in.h>
 
+#include "bscconfig.h"
+
 #include <osmocom/core/msgb.h>
 #include <osmocom/gsm/tlv.h>
 #include <openbsc/debug.h>
@@ -279,7 +281,12 @@ static void gsm340_gen_scts(uint8_t *scts, time_t time)
 	*scts++ = bcdify(tm->tm_hour);
 	*scts++ = bcdify(tm->tm_min);
 	*scts++ = bcdify(tm->tm_sec);
+#ifdef HAVE_TM_GMTOFF_IN_TM
 	*scts++ = bcdify(tm->tm_gmtoff/(60*15));
+#else
+#warning find a portable way to obtain timezone offset
+	*scts++ = 0;
+#endif
 }
 
 /* Decode 03.40 TP-SCTS (into utc/gmt timestamp) */
@@ -300,7 +307,9 @@ static time_t gsm340_scts(uint8_t *scts)
 	tm.tm_sec  = unbcdify(*scts++);
 	/* according to gsm 03.40 time zone is
 	   "expressed in quarters of an hour" */
+#ifdef HAVE_TM_GMTOFF_IN_TM
 	tm.tm_gmtoff = unbcdify(*scts++) * 15*60;
+#endif
 
 	return mktime(&tm);
 }