Add an ISO dist target back for system sim testing

Some system simulators have no network support or the network support is a
pain to configure.  An ISO dist package allows easier testing.  The ISO
target is now a separate target to avoid increasing the util requirements
for e.g. Cygwin builds.

Makefile

@@ -248,6 +248,7 @@ clean:
 	@rm -f duk.raw dukd.raw duk.vg dukd.vg duk dukd
 	@rm -f libduktape*.so*
 	@rm -f duktape-*.tar.*
+	@rm -f duktape-*.iso
 	@rm -f doc/*.html
 	@rm -f src/*.pyc
 	@rm -rf massif.out.* ms_print.tmp.*
@@ -779,6 +780,11 @@ dist-src:	dist
 	cp duktape-$(DUK_VERSION_FORMATTED).tar.xz duktape-$(DUK_VERSION_FORMATTED)-$(BUILD_DATETIME)-$(GIT_DESCRIBE).tar.xz
 	rm -rf duktape-$(DUK_VERSION_FORMATTED)
 
+# ISO target is useful with some system emulators with no network access
+.PHONY: dist-iso
+dist-iso:	dist-src
+	mkisofs -input-charset utf-8 -o duktape-$(DUK_VERSION_FORMATTED)-$(BUILD_DATETIME)-$(GIT_DESCRIBE).iso duktape-$(DUK_VERSION_FORMATTED)-$(BUILD_DATETIME)-$(GIT_DESCRIBE).tar.gz
+
 .PHONY: tidy-site
 tidy-site:
 	for i in website/*/*.html; do echo "*** Checking $$i"; tidy -q -e -xml $$i; done