Makefile: Split out coverage into a shell script

coverage_all.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+TARGETFILE="$1"
+
+go list ./... | while read pkg; do
+    go test -covermode=count -coverprofile=$(base64 <<< $pkg).cov $pkg
+done
+
+echo "mode: count" > $TARGETFILE
+tail -q -n +2 *.cov >> $TARGETFILE