balena-engine: Patch out hardcoded CC for cross-compile

Port of meta-virtualization/docker commit:
https://git.yoctoproject.org/cgit/cgit.cgi/meta-virtualization/commit/recipes-containers/docker/docker-ce_git.bb?id=e7787cb01be91d3798594687a475d5b085f29ede

Since commit applied in moby [61a3285 Support cross-compile for arm]
it hardcoded var-CC to support cross-compile for arm

Correct it with "${parameter:-word}" format, it is helpful for user
define toolchains

(Use Default Values.  If parameter is unset or null, the expansion of
word is substituted.  Otherwise, the value of parameter is substituted.)

moby/moby@61a3285

meta-balena-common/recipes-containers/balena/balena/0001-imporve-hardcoded-CC-on-cross-compile-docker-ce.patch

@@ -0,0 +1,60 @@
+From 1263fdb50a540e9db742694b7cee08284ad986d0 Mon Sep 17 00:00:00 2001
+From: Hongxu Jia <[email protected]>
+Date: Wed, 17 Jul 2019 17:34:04 +0800
+Subject: [PATCH] imporve hardcoded CC on cross compile
+
+Since commit applied in moby [61a3285 Support cross-compile for arm]
+it hardcoded var-CC to support cross-compile for arm
+
+Correct it with "${parameter:-word}" format, it is helpful for user
+define toolchains
+
+(Use Default Values.  If parameter is unset or null, the expansion of
+word is substituted.  Otherwise, the value of parameter is substituted.)
+
+Upstream-Status: Submitted [https://github.com/moby/moby/pull/39546]
+
+Signed-off-by: Hongxu Jia <[email protected]>
+---
+ hack/make/.binary | 10 +++++-----
+ 1 file changed, 5 insertions(+), 5 deletions(-)
+
+diff --git a/src/import/hack/make/.binary b/src/import/hack/make/.binary
+index 53de6749e5..66f4ca05f3 100644
+--- a/src/import/hack/make/.binary
++++ b/src/import/hack/make/.binary
+@@ -44,27 +44,27 @@ if [ "$(go env GOOS)/$(go env GOARCH)" != "$(go env GOHOSTOS)/$(go env GOHOSTARC
+	# must be cross-compiling!
+	case "$(go env GOOS)/$(go env GOARCH)" in
+		windows/amd64)
+-			export CC=x86_64-w64-mingw32-gcc
++			export CC="${CC:-x86_64-w64-mingw32-gcc}"
+			export CGO_ENABLED=1
+			;;
+		linux/arm)
+			case "${GOARM}" in
+			5|"")
+-				export CC=arm-linux-gnueabi-gcc
++				export CC="${CC:-arm-linux-gnueabi-gcc}"
+				export CGO_ENABLED=1
+				;;
+			7)
+-				export CC=arm-linux-gnueabihf-gcc
++				export CC="${CC:-arm-linux-gnueabihf-gcc}"
+				export CGO_ENABLED=1
+				;;
+			esac
+			;;
+		linux/arm64)
+-			export CC=aarch64-linux-gnu-gcc
++			export CC="${CC:-aarch64-linux-gnu-gcc}"
+			export CGO_ENABLED=1
+			;;
+		linux/amd64)
+-			export CC=x86_64-linux-gnu-gcc
++			export CC="${CC:-x86_64-linux-gnu-gcc}"
+			export CGO_ENABLED=1
+			;;
+	esac
+--
+2.23.0

meta-balena-common/recipes-containers/balena/balena_git.bb

@@ -25,6 +25,7 @@ SRC_URI = "\
 	file://var-lib-docker.mount \
 	file://balena.conf.systemd \
 	file://balena-tmpfiles.conf \
+	file://0001-imporve-hardcoded-CC-on-cross-compile-docker-ce.patch \
 	"
 S = "${WORKDIR}/git"