move unixDie() so it is generally available

navcat.cc

@@ -26,11 +26,6 @@ using namespace std;
 
 extern const char* g_gitHash;
 
-void unixDie(const std::string& str)
-{
-  throw std::runtime_error(str+string(": ")+string(strerror(errno)));
-}
-
 time_t parseTime(std::string_view in)
 {
   time_t now=time(0);

navmon.cc

@@ -351,3 +351,8 @@ size_t writen2(int fd, const void *buf, size_t count)
 
   return count;
 }
+
+void unixDie(const std::string& reason)
+{
+  throw std::runtime_error(reason+": "+strerror(errno));
+}

navmon.hh

@@ -78,3 +78,4 @@ double utcFromGPS(int wn, double tow);
 
 std::string makeHexDump(const std::string& str);
 size_t writen2(int fd, const void *buf, size_t count);
+void unixDie(const std::string& reason);