set RPATH (only to be used on ELF platforms)

(currently nothing in LO actually links libpython3.so)

diff -ru python3.orig/Makefile.pre.in python3/Makefile.pre.in
--- python3.orig/Makefile.pre.in	2015-07-26 20:29:07.126194320 +0200
+++ python3/Makefile.pre.in	2015-07-26 20:37:21.814227530 +0200
@@ -566,7 +566,7 @@
 
 # Build the interpreter
 $(BUILDPYTHON):	Programs/python.o $(LIBRARY) $(LDLIBRARY) $(PY3LIBRARY)
-	$(LINKCC) $(PY_CORE_LDFLAGS) $(LINKFORSHARED) -o $@ Programs/python.o $(BLDLIBRARY) $(LIBS) $(MODLIBS) $(SYSLIBS)
+	$(LINKCC) $(PY_CORE_LDFLAGS) $(LINKFORSHARED) -o $@ Programs/python.o $(BLDLIBRARY) $(LIBS) $(MODLIBS) $(SYSLIBS) -Wl,-rpath,\$$ORIGIN
 
 platform: $(BUILDPYTHON) pybuilddir.txt
 	$(RUNSHARED) $(PYTHON_FOR_BUILD) -c 'import sys ; from sysconfig import get_platform ; print("%s-%d.%d" % (get_platform(), *sys.version_info[:2]))' >platform
@@ -628,7 +628,7 @@
 	fi
 
 libpython3.so:	libpython$(LDVERSION).so
-	$(BLDSHARED) $(NO_AS_NEEDED) -o $@ -Wl,-h$@ $^
+	$(BLDSHARED) $(NO_AS_NEEDED) -o $@ -Wl,-h$@ $^ -Wl,-rpath,\$$ORIGIN
 
 libpython$(LDVERSION).dylib: $(LIBRARY_OBJS)
 	 $(CC) -dynamiclib -Wl,-single_module $(PY_CORE_LDFLAGS) -undefined dynamic_lookup -Wl,-install_name,$(prefix)/lib/libpython$(LDVERSION).dylib -Wl,-compatibility_version,$(VERSION) -Wl,-current_version,$(VERSION) -o $@ $(LIBRARY_OBJS) $(DTRACE_OBJS) $(SHLIBS) $(LIBC) $(LIBM); \