ltlcheck: Record translation time.

* lib/gethrxtime.h, lib/xtime.h: Add extern "C".
* src/bin/Makefile.am (ltlcheck_LDADD): Use LIB_GETHRXTIME.
* src/bin/ltlcheck.cc: Use gethrxtime() to record translation time.

lib/gethrxtime.h

@@ -22,6 +22,10 @@
 
 # include "xtime.h"
 
+#ifdef  __cplusplus
+extern "C" {
+#endif
+
 /* Get the current time, as a count of the number of nanoseconds since
    an arbitrary epoch (e.g., the system boot time).  Prefer a
    high-resolution clock that is not subject to resetting or
@@ -34,4 +38,8 @@ static inline xtime_t gethrxtime (void) { return gethrtime (); }
 xtime_t gethrxtime (void);
 # endif
 
+#ifdef  __cplusplus
+}
+#endif
+
 #endif

lib/xtime.h

@@ -37,6 +37,10 @@ typedef long int xtime_t;
 #  endif
 # endif
 
+#ifdef  __cplusplus
+extern "C" {
+#endif
+
 /* Return an extended time value that contains S seconds and NS
    nanoseconds, without any overflow checking.  */
 static inline xtime_t
@@ -83,4 +87,8 @@ xtime_nsec (xtime_t t)
   return ns;
 }
 
+#ifdef  __cplusplus
+}
+#endif
+
 #endif