[arm64ilp32] Build a linux-libc-dev package (Closes: #874536)

debian/changelog

@@ -5,6 +5,7 @@ linux (4.13.3-1~exp1) UNRELEASED; urgency=medium
 
   [ Ben Hutchings ]
   * [armhf,arm64] mmc: Enable MMC_BCM2835 (Closes: #845422)
+  * [arm64ilp32] Build a linux-libc-dev package (Closes: #874536)
 
   [ Uwe Kleine-König ]
   * [arm64] really enable NET_DSA_MV88E6XXX for Espressobin

debian/config/arm64ilp32/defines

@@ -0,0 +1,5 @@
+[base]
+kernel-arch: arm64
+featuresets:
+# empty; arm64ilp32 must be part of a multiarch installation with an arm64
+# kernel

debian/config/defines

@@ -59,6 +59,7 @@ arches:
  alpha
  amd64
  arm64
+ arm64ilp32
  armel
  armhf
  hppa