Try to build multiple compiler versions

.drone.jsonnet

@@ -1,3 +1,9 @@
+local test_compiler_version(version) = [
+    "cd code/compiler/%(version)",
+    "mkdir build && cd build",
+    "cd .."
+]
+
 {
     "kind": "pipeline",
     "type": "docker",
@@ -6,10 +12,7 @@
         {
             "name": "test-compiler",
             "image": "gcc",
-            "commands": [
-                "cd code/compiler/09",
-                "mkdir build && cd build"
-            ]
+            "commands": std.flatMap(test_compiler_version, [4,5,6,7,8,9])
         }
     ]
 }