debian/signing_templates/rules: Use /usr/share/dpkg/architecture.mk

Fixes lintian warning debian-rules-sets-dpkg-architecture-variable
for the signed source packages.

debian/changelog

@@ -24,6 +24,7 @@ linux (4.19~rc3-1~exp2) UNRELEASED; urgency=medium
   * debian/control: Build-depend on texlive-latex-{base,extra}, dvipng for
     linux-doc
   * debian/rules{,.real}: Use /usr/share/dpkg/architecture.mk
+  * debian/signing_templates/rules: Use /usr/share/dpkg/architecture.mk
 
  -- Ben Hutchings <ben@decadent.org.uk>  Mon, 10 Sep 2018 22:25:53 +0100
 

debian/signing_templates/rules

@@ -1,7 +1,7 @@
 #!/usr/bin/make -f
 SHELL := sh -e
 
-DEB_HOST_ARCH  := $(shell dpkg-architecture -qDEB_HOST_ARCH)
+include /usr/share/dpkg/architecture.mk
 
 build: build-arch build-indep
 build-arch: