makepkg: fix build

Without docbook-xsl and the corresponding XML_CATALOG_FILES in the
environment, xsltproc(1) attempts to load .xsl files, e.g.,
http://docbook.sourceforge.net/release/xsl/current/html/lists.xsl, from
the Internet, and when the build is parallelized, that is, multiple
xsltproc processes attempt to fetch the same .xsl file at the same time
and presumably write to the same location, a race condition is triggered
and all processes exit with status 5.

An alternative fix is ENV.deparallelize, but having to fetch .xsl files
on the go and thus preventing offline builds is probably something to be
frowned upon.

Closes #6402.

Signed-off-by: Tomasz Pajor <[email protected]>

Formula/makepkg.rb

@@ -4,6 +4,8 @@ class Makepkg < Formula
   url "https://projects.archlinux.org/git/pacman.git",
       :tag => "v5.0.1",
       :revision => "f38de43eb68f1d9c577b4378310640c1eaa93338"
+  revision 1
+
   head "https://projects.archlinux.org/git/pacman.git"
 
   bottle do
@@ -18,7 +20,7 @@ class Makepkg < Formula
 
   depends_on "automake" => :build
   depends_on "autoconf" => :build
-  depends_on "asciidoc" => :build
+  depends_on "asciidoc" => ["with-docbook-xsl", :build]
   depends_on "libtool" => :build
   depends_on "pkg-config" => :build
   depends_on "libarchive"
@@ -29,6 +31,8 @@ class Makepkg < Formula
   depends_on "gpgme" => :optional
 
   def install
+    ENV["XML_CATALOG_FILES"] = etc/"xml/catalog"
+
     system "./autogen.sh"
     system "./configure", "--disable-dependency-tracking",
                           "--prefix=#{prefix}",