Don't build j1939 for Android

This library uses if_nameindex symbol, not available at this system.

CMakeLists.txt

@@ -63,6 +63,10 @@ set(PROGRAMS
 
 if(NOT ANDROID)
   list(APPEND PROGRAMS ${PROGRAMS_J1939})
+
+  add_library(j1939 STATIC
+      libj1939.c
+  )
 endif()
 
 add_library(can STATIC
@@ -70,10 +74,6 @@ add_library(can STATIC
     canframelen.c
 )
 
-add_library(j1939 STATIC
-    libj1939.c
-)
-
 foreach(name ${PROGRAMS})
   add_executable(${name} ${name}.c)