Check for host system instead of target at build time

Using AC_CANONICAL_TARGET is needed when wanting to support building
cross-compiling software. But there's too many assumptions in dpkg that
the host system in dpkg-dev is going to match the build system.

m4/arch.m4

@@ -3,22 +3,22 @@
 # Use dpkg-architecture from the source tree to set sh_var using DEB_VAR for
 # the target architecture, to avoid duplicating its logic.
 AC_DEFUN([_DPKG_ARCHITECTURE], [
-AC_REQUIRE([AC_CANONICAL_TARGET])dnl
+AC_REQUIRE([AC_CANONICAL_HOST])dnl
 $2=`cd $srcdir/scripts; \
-    PERL5LIB=$(pwd) ./dpkg-architecture.pl -t$target -q$1 2>/dev/null`
+    PERL5LIB=$(pwd) ./dpkg-architecture.pl -t$host -q$1 2>/dev/null`
 ])# _DPKG_ARCHITECURE
 
 # DPKG_CPU_TYPE
 # -------------
-# Parse the target cpu name and check it against the cputable to determine
+# Parse the host cpu name and check it against the cputable to determine
 # the Debian name for it.  Sets ARCHITECTURE_CPU.
 AC_DEFUN([DPKG_CPU_TYPE],
 [AC_MSG_CHECKING([dpkg cpu type])
 _DPKG_ARCHITECTURE([DEB_HOST_ARCH_CPU], [cpu_type])
 if test "x$cpu_type" = "x"; then
-	cpu_type=$target_cpu
+	cpu_type=$host_cpu
 	AC_MSG_RESULT([$cpu_type])
-	AC_MSG_WARN([$target_cpu not found in cputable])
+	AC_MSG_WARN([$host_cpu not found in cputable])
 else
 	AC_MSG_RESULT([$cpu_type])
 fi
@@ -28,15 +28,15 @@ AC_DEFINE_UNQUOTED(ARCHITECTURE_CPU, "${cpu_type}",
 
 # DPKG_OS_TYPE
 # ------------
-# Parse the target operating system name and check it against a list of
+# Parse the host operating system name and check it against a list of
 # special cases to determine what type it is.  Sets ARCHITECTURE_OS.
 AC_DEFUN([DPKG_OS_TYPE],
 [AC_MSG_CHECKING([dpkg operating system type])
 _DPKG_ARCHITECTURE([DEB_HOST_ARCH_OS], [os_type])
 if test "x$os_type" = "x"; then
-	os_type=$target_os
+	os_type=$host_os
 	AC_MSG_RESULT([$os_type])
-	AC_MSG_WARN([$target_os not found in ostable])
+	AC_MSG_WARN([$host_os not found in ostable])
 else
 	AC_MSG_RESULT([$os_type])
 fi
@@ -46,7 +46,7 @@ AC_DEFINE_UNQUOTED(ARCHITECTURE_OS, "${os_type}",
 
 # DPKG_ARCHITECTURE
 # ------------------------
-# Determine the Debian name for the target operating system,
+# Determine the Debian name for the host operating system,
 # sets ARCHITECTURE.
 AC_DEFUN([DPKG_ARCHITECTURE],
 [DPKG_CPU_TYPE