Add global LM_SIZEOF_OFF_T variable to report compile-time size of off_t

Author: Chad Trabant

ChangeLog

@@ -1,3 +1,7 @@
+2017.118: 2.19.4
+	- Add global LM_SIZEOF_OFF_T variable that is set to the size of
+	the off_t data type as determined at compile time.
+
 2017.075: 2.19.3
 	- Add missing public, global symbols to libmseed.map, thanks
 	to Elliott Sales de Andrade.

libmseed.h

@@ -28,8 +28,8 @@
 extern "C" {
 #endif
 
-#define LIBMSEED_VERSION "2.19.3"
-#define LIBMSEED_RELEASE "2017.075"
+#define LIBMSEED_VERSION "2.19.4"
+#define LIBMSEED_RELEASE "2017.118"
 
 /* C99 standard headers */
 #include <stdlib.h>
@@ -118,6 +118,8 @@ extern "C" {
   #include <inttypes.h>
 #endif
 
+extern int LM_SIZEOF_OFF_T;  /* Size of off_t data type determined at build time */
+
 #define MINRECLEN   128      /* Minimum Mini-SEED record length, 2^7 bytes */
                              /* Note: the SEED specification minimum is 256 */
 #define MAXRECLEN   1048576  /* Maximum Mini-SEED record length, 2^20 bytes */

libmseed.map

@@ -10,6 +10,7 @@
       unpackdatabyteorder;
       unpackencodingformat;
       unpackencodingfallback;
+      LM_SIZEOF_OFF_T;
 
   local:
       *;

lmplatform.c

@@ -3,14 +3,17 @@
  *
  * Platform portability routines.
  *
- * modified: 2010.304
+ * modified: 2017.118
  ***************************************************************************/
 
 /* Define _LARGEFILE_SOURCE to get ftello/fseeko on some systems (Linux) */
 #define _LARGEFILE_SOURCE 1
 
 #include "libmseed.h"
 
+/* Size of off_t data type as determined at build time */
+int LM_SIZEOF_OFF_T = sizeof(off_t);
+
 /***************************************************************************
  * lmp_ftello:
  *