Make VPATH build work

Sometimes, you may need to distinguish the source tree and the build tree, when you want to keep the source tree uncluttered, or you need to build the source with several different configurations, or even your source tree is read only. This feature is called VPATH build and the patch is to make this work. A typical example is as below (Note that the "build" directory can be any name and in any place):

Then everything you got from the make will reside in "build" directory.

---
 Makefile.am |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

index eca8eee..bd74fb7 100644
@@ -374,11 +374,11 @@ $(src_ofonod_OBJECTS) $(unit_objects): $(local_headers)
 
 include/ofono/version.h: include/version.h
 	$(AM_V_at)$(MKDIR_P) include/ofono
-	$(AM_V_GEN)$(LN_S) $(abs_top_builddir)/$< $@
+	$(AM_V_GEN)$(LN_S) $(abs_builddir)/$< $@
 
 include/ofono/%.h: include/%.h
 	$(AM_V_at)$(MKDIR_P) include/ofono
-	$(AM_V_GEN)$(LN_S) $(abs_top_srcdir)/$< $@
+	$(AM_V_GEN)$(LN_S) $(abs_builddir)/$< $@
 
 clean-local: include/ofono
 	@$(RM) -r $<

1.6.3.3