chore: Enable ccache for travis/Linux

.travis.yml

@@ -5,8 +5,9 @@ services:
   - docker
 
 cache:
-  directories:
-  - $HOME/Library/Caches/Homebrew
+  - ccache: true
+  - directories:
+      - $HOME/Library/Caches/Homebrew
 
 matrix:
   include:

CMakeLists.txt

@@ -5,6 +5,11 @@ set(CMAKE_OSX_DEPLOYMENT_TARGET "10.9"
     CACHE STRING "Minimum macOS deployment version"
 )
 
+find_program(CCACHE_PROGRAM ccache)
+if(CCACHE_PROGRAM)
+    set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE "${CCACHE_PROGRAM}")
+endif()
+
 project(firewallbuilder LANGUAGES CXX C)
 
 ### Version variables and include file

docker/Dockerfile.ubuntu_16.04

@@ -13,7 +13,8 @@ RUN apt-get update && apt-get install -y \
     nsis \
     cmake \
     git \
-    qt5-default
+    qt5-default \
+    ccache
 
 WORKDIR /
 CMD ["bash"]

docker/Dockerfile.ubuntu_18.04

@@ -13,7 +13,8 @@ RUN apt-get update && apt-get install -y \
     nsis \
     cmake \
     git \
-    qt5-default
+    qt5-default \
+    ccache
 
 WORKDIR /
 CMD ["bash"]