makefile export: create .link_options.txt with echo

$(file > $@.in, $(filter %.o, $^)) is not supported in GNU Make 3.81.
Create the linker response file with pipe redirect from echo command.
This is tested with Cygwin make and make 3.8.1 shipped with macOS.

(cherry picked from commit 6918e6a76b)

Revert "Fixed problem with overlong command line."

This reverts commit dd02ac09a1.

See also https://github.com/ARMmbed/mbed-os/pull/12646#issuecomment-602058273

tools/export/makefile/Makefile.tmpl

@@ -135,7 +135,7 @@ $(PROJECT).link_script{{link_script_ext}}: $(LINKER_SCRIPT)
 
 {% block target_project_elf %}
 $(PROJECT).elf: $(OBJECTS) $(SYS_OBJECTS) {% if pp_cmd -%} $(PROJECT).link_script{{link_script_ext}} {% else%} $(LINKER_SCRIPT) {% endif %}
-	$(file > .link_options.txt,$(filter %.o, $^)
+	+@echo "$(filter %.o, $^)" > .link_options.txt
 	+@echo "link: $(notdir $@)"
 	@$(LD) $(LD_FLAGS) {{link_script_option}} $(filter-out %.o, $^) $(LIBRARY_PATHS) --output $@ {{response_option}}.link_options.txt $(LIBRARIES) $(LD_SYS_LIBS)
 {% endblock %}