Add platform and its components to docker version output

The Server section of version output is now composed of an Engine
component and potentially more, based on what the /version endpoint
returns.

Signed-off-by: Tibor Vass <tibor@docker.com>

scripts/build/.variables

@@ -1,15 +1,22 @@
 #!/usr/bin/env bash
 set -eu
 
+PLATFORM=${PLATFORM:-}
 VERSION=${VERSION:-"unknown-version"}
 GITCOMMIT=${GITCOMMIT:-$(git rev-parse --short HEAD 2> /dev/null || true)}
 BUILDTIME=${BUILDTIME:-$(date --utc --rfc-3339 ns 2> /dev/null | sed -e 's/ /T/')}
 
+PLATFORM_LDFLAGS=
+if test -n "${PLATFORM}"; then
+	PLATFORM_LDFLAGS="-X \"github.com/docker/cli/cli.PlatformName=${PLATFORM}\""
+fi
+
 export LDFLAGS="\
     -w \
-    -X github.com/docker/cli/cli.GitCommit=${GITCOMMIT} \
-    -X github.com/docker/cli/cli.BuildTime=${BUILDTIME} \
-    -X github.com/docker/cli/cli.Version=${VERSION} \
+    ${PLATFORM_LDFLAGS} \
+    -X \"github.com/docker/cli/cli.GitCommit=${GITCOMMIT}\" \
+    -X \"github.com/docker/cli/cli.BuildTime=${BUILDTIME}\" \
+    -X \"github.com/docker/cli/cli.Version=${VERSION}\" \
     ${LDFLAGS:-} \
 "