app-vim/extra-syntax: fix untested ebuild that failed to build for three months

Gentoo-bug: 592162

Package-Manager: portage-2.3.2

app-vim/extra-syntax/extra-syntax-4-r1.ebuild

@@ -34,6 +34,8 @@ RDEPEND="
 	app-vim/xquery-syntax
 	app-vim/xsl-syntax"
 
+S=${WORKDIR}
+
 src_install() {
 	:
 }