add build cache

.gitlab-ci.yml

@@ -108,6 +108,10 @@ windows_exec:
     - mat_windows
   variables:
     irrklang_pro: '1'
+  cache:
+    paths:
+      - bin/
+      - obj/
   script:
     - git submodule update --init
     - bash -c 'cp -rf premake/* .'
@@ -126,6 +130,10 @@ linux_exec:
   dependencies:
     - mat_irrklang
     - mat_linux
+  cache:
+    paths:
+      - bin/
+      - obj/
   script:
     - apt update; apt -y install git build-essential libfreetype6-dev libevent-dev libsqlite3-dev libgl1-mesa-dev libglu-dev liblua5.3-dev libxxf86vm-dev
     - git submodule update --init