Add ccache to github actions

.github/workflows/compile_nuttx.yml

@@ -1,4 +1,4 @@
-name: compile nuttx
+name: nuttx
 
 on:
   push:
@@ -55,8 +55,19 @@ jobs:
     - uses: actions/checkout@v1
       with:
         token: ${{secrets.ACCESS_TOKEN}}
+    - uses: actions/cache@v1.1.0
+      id: ccache-persistence
+      with:
+        path: ~/.ccache
+        key: ccache-nuttx-${{matrix.config}}
+        restore-keys: |
+          ccache-nuttx-${{matrix.config}}
+    - name: setup ccache
+      run: mkdir -p ~/.ccache && echo "max_size = 300M" > ~/.ccache/ccache.conf && ccache -z && ccache -s
     - name: make ${{matrix.config}}
       run: make ${{matrix.config}}
+    - name: ccache post-run
+      run: ccache -s && ccache -z
     - name: Upload px4 package
       uses: actions/upload-artifact@v1
       with: