travis: Cross-compile ARM builds

index b0d0fb156..29da4d29e 100755
@@ -26,10 +26,21 @@ build_32()
 
 build_native()
 {
-	echo "===== native in tree build into $PREFIX ====="
+	echo "===== native in-tree build into $PREFIX ====="
 	build_in_tree
 }
 
+build_cross()
+{
+	local host="${CROSS_COMPILE%-}"
+	[ -n "$host" ] || host="${CC%-gcc}"
+	[ -n "$host" ] || \
+		{ echo "Missing CROSS_COMPILE and CC variables. You need to set at least one" >&2; exit 1; }
+
+	echo "===== cross-compile ${host} in-tree build into $PREFIX ====="
+	build_in_tree "--host=$host" CROSS_COMPILE="${host}-"
+}
+
 build_out_tree()
 {
 	local tree="$PWD"

@@ -90,6 +101,7 @@ Options:
 
 BUILD TYPES:
 32      32-bit in-tree build
+cross   cross-compile in-tree build (requires to set CROSS_COMPILE or CC variable)
 native  native in-tree build
 out     out-of-tree build
 

@@ -100,6 +112,7 @@ EOF
 case "$1" in
 	-h|--help|help) usage; exit 0;;
 	32) build="build_32";;
+	cross) build="build_cross";;
 	out) build="build_out_tree";;
 	*) build="build_native";;
 esac

index 2087e4174..74838be7c 100644
@@ -4,14 +4,6 @@ matrix:
     include:
 
         # normal native in-tree builds
-        - os: linux
-          env: BUILD="native" INSTALL_PACKAGES="$BUILD"
-          compiler: gcc-4.9
-          addons:
-              apt:
-                  sources: ['ubuntu-toolchain-r-test']
-                  packages: ['gcc-4.9']
-
         - os: linux
           env: BUILD="native" INSTALL_PACKAGES="$BUILD"
           compiler: gcc-5

@@ -20,14 +12,6 @@ matrix:
                   sources: ['ubuntu-toolchain-r-test']
                   packages: ['gcc-5']
 
-        - os: linux
-          env: BUILD="native" INSTALL_PACKAGES="$BUILD"
-          compiler: gcc-6
-          addons:
-              apt:
-                  sources: ['ubuntu-toolchain-r-test']
-                  packages: ['gcc-6']
-
         - os: linux
           env: BUILD="native" INSTALL_PACKAGES="$BUILD"
           compiler: gcc-7

@@ -87,6 +71,21 @@ matrix:
                   sources: ['ubuntu-toolchain-r-test']
                   packages: ['gcc-7']
 
+        # cross-compile ARM builds
+        - os: linux
+          env: BUILD="cross" INSTALL_PACKAGES="$BUILD"
+          compiler: arm-linux-gnueabihf-gcc
+          addons:
+              apt:
+                  packages: ['gcc-arm-linux-gnueabihf', 'libc6-dev-armhf-cross']
+
+        - os: linux
+          env: BUILD="cross" INSTALL_PACKAGES="$BUILD"
+          compiler: aarch64-linux-gnu-gcc
+          addons:
+              apt:
+                  packages: ['gcc-aarch64-linux-gnu', 'libc6-dev-arm64-cross']
+
 notifications:
     email:
         secure: "b/xcA/K5OyQvPPnd0PRahTH5LJu8lgz8goGHvhXpHo+ZPsPgTDXNFo5cX9fSOkMuFKeoW8iGl0wOgK2+ptc8mbYDw277K4RFIHRHeV/KIoE1EzjQnEFiL8J0oHCAvDj12o0AXeriTyY9gICXKbR31Br6Zh5eKViDJe2OAGeHeDU="

@@ -95,7 +94,7 @@ before_install:
     # installing / removing dependencies
     - if [ "$INSTALL_PACKAGES" = "" ]; then
           sudo apt remove $(cat .travis.packages_native | grep -v -e 'libc6' -e 'libc6-dev' -e 'linux-libc-dev' -e 'libacl1')
-      ; else
+      ; elif [ "$INSTALL_PACKAGES" != "cross" ]; then
           sudo apt install -qq $(cat .travis.packages_native)
       ; fi