Add eval $(opam env) for osx vscode task (#11801)

.vscode/tasks.json

@@ -5,6 +5,9 @@
 			"label": "make: haxe",
 			"type": "shell",
 			"command": "make ADD_REVISION=1 -s -j haxe",
+			"osx": {
+				"command": "eval $(opam env) && make ADD_REVISION=1 -s -j haxe",
+			},
 			"windows": {
 				"command": "make ADD_REVISION=1 -f Makefile.win -s -j haxe"
 			},
@@ -48,4 +51,4 @@
 			"problemMatcher": []
 		}
 	]
-}
+}