debian/rules{,.real}: Use /usr/share/dpkg/architecture.mk

Currently we don't set all the architecture variables, so direct use
of these makefiles (not under dpkg-architecture or dpkg-buildpackage)
may fail.

In case ARCH and DEB_HOST_ARCH don't match in rules.real, we really
should fail, so add an explicit check for that.

This also fixes lintian warning
debian-rules-sets-dpkg-architecture-variable.

debian/changelog

@@ -23,6 +23,7 @@ linux (4.19~rc3-1~exp2) UNRELEASED; urgency=medium
   * tools: turbostat: Add checks for failure of fgets() and fscanf()
   * debian/control: Build-depend on texlive-latex-{base,extra}, dvipng for
     linux-doc
+  * debian/rules{,.real}: Use /usr/share/dpkg/architecture.mk
 
  -- Ben Hutchings <ben@decadent.org.uk>  Mon, 10 Sep 2018 22:25:53 +0100
 

debian/rules

@@ -1,12 +1,13 @@
 #!/usr/bin/make -f
 
 SHELL    := sh -e
-DEB_HOST_ARCH := $(shell dpkg-architecture -qDEB_HOST_ARCH)
 SOURCE := $(shell dpkg-parsechangelog -SSource)
 VERSION := $(shell dpkg-parsechangelog -SVersion)
 VERSION_UPSTREAM := $(shell echo "$(VERSION)" | sed -e 's,-[^-]*$$,,')
 VERSION_BINNMU := $(shell echo "$(VERSION)" | sed -rne 's,.*\+b([0-9]+)$$,\1,p')
 
+include /usr/share/dpkg/architecture.mk
+
 include debian/rules.defs
 
 ifneq (,$(filter parallel=%,$(DEB_BUILD_OPTIONS)))

debian/rules.real

@@ -16,8 +16,16 @@ ifeq ($(DISTRIBUTOR),)
 DISTRIBUTOR := Debian
 endif
 
+include /usr/share/dpkg/architecture.mk
+
 include debian/rules.defs
 
+ifdef ARCH
+  ifneq ($(DEB_HOST_ARCH),$(ARCH))
+    $(error Attempting to build a $(ARCH) target but host architecture is $(DEB_HOST_ARCH).  Use dpkg-architecture to override the host architecture)
+  endif
+endif
+
 ifdef OVERRIDE_HOST_TYPE
   CROSS_COMPILE := $(OVERRIDE_HOST_TYPE)-
 else ifneq ($(DEB_BUILD_ARCH),$(DEB_HOST_ARCH))