See if _TIME_BITS_64 works on 32-bit bit builds to fix 2038 problem.

https://github.com/Hamlib/Hamlib/issues/1478

Makefile.am

@@ -28,4 +28,4 @@ DIST_SUBDIRS = macros include lib src c++ bindings tests doc android scripts rot
 	security $(BACKEND_LIST) $(RIG_BACKEND_LIST) $(ROT_BACKEND_LIST) $(AMP_BACKEND_LIST)
 
 # Install any third party macros into our tree for distribution
-ACLOCAL_AMFLAGS = -I macros --install
+ACLOCAL_AMFLAGS = -I macros --install -D_TIME_BITS=64