Check in CMake config that we are building for 64bit architecture

For a long time we haven't officially supported 32bit architectures but
not really disabled them. But this is giving us more problems lately and
we can't test on 32 bit systems anyway, so this now gives us an up front
check.

Author: joto

CMakeLists.txt

@@ -16,6 +16,10 @@ else()
     set(ENABLE_INSTALL OFF)
 endif()
 
+if (NOT ${CMAKE_SIZEOF_VOID_P} EQUAL 8)
+    message(FATAL_ERROR "osm2pgsql needs a 64 bit architecture")
+endif()
+
 if (WIN32)
     set(DEFAULT_STYLE "default.style" CACHE STRING "Default style used unless one is given on the command line")
 else()