build: allow custom PackageMaker path

Make PACKAGEMAKER customizable because PackageMaker is not necessarily
installed in /Developer on OSX anymore.

PR-URL: https://github.com/joyent/node/pull/9377
Reviewed-By: Timothy J Fontaine <tjfontaine@gmail.com>

Makefile

@@ -219,7 +219,7 @@ BINARYNAME=$(TARNAME)-$(PLATFORM)-$(ARCH)
 BINARYTAR=$(BINARYNAME).tar
 XZ=$(shell which xz > /dev/null 2>&1; echo $$?)
 PKG=out/$(TARNAME).pkg
-packagemaker=/Developer/Applications/Utilities/PackageMaker.app/Contents/MacOS/PackageMaker
+PACKAGEMAKER ?= /Developer/Applications/Utilities/PackageMaker.app/Contents/MacOS/PackageMaker
 
 PKGSRC=iojs-$(DESTCPU)-$(RAWVER).tgz
 ifdef NIGHTLY
@@ -270,7 +270,7 @@ $(PKG): release-only
 	mv $(PKGDIR)/usr/local/bin/iojs-universal $(PKGDIR)/usr/local/bin/iojs
 	rm -rf $(PKGDIR)/32
 	cat tools/osx-pkg.pmdoc/index.xml.tmpl | sed -e 's|__iojsversion__|'$(FULLVERSION)'|g' | sed -e 's|__npmversion__|'$(NPMVERSION)'|g' > tools/osx-pkg.pmdoc/index.xml
-	$(packagemaker) \
+	$(PACKAGEMAKER) \
 		--id "org.nodejs.Node" \
 		--doc tools/osx-pkg.pmdoc \
 		--out $(PKG)