travis: use cache

* travis: cache clang-format installation

* travis: indent

* travis: use user paths for caching

* travis: cache go build results

* travis: use system clang-format

* travis: remove custom libstdc++ installation

Fixes #1252

.travis.yml

@@ -5,24 +5,18 @@ go:
   - "1.11"
   - "1.12"
 
+cache:
+  directories:
+    - $HOME/.cache/go-build
+    - $HOME/gopath/pkg/mod
+
 before_install:
-  - echo $PATH
-  - export PATH=`echo $PATH | sed -e 's/:\/usr\/local\/clang-[0-9].[0-9].[0-9]\/bin//'`
   # xenial packages are broken and do no allow to cross-compile for both 386 and arm.
   # 386 requires gcc-multilib installed and arm requires gcc-arm-linux-gnueabi,
   # but these packages are conflicting. This is a hacky way to install 386 headers.
   - sudo dpkg --add-architecture i386
   - sudo apt-get update
   - sudo apt-get install -y -q linux-libc-dev:i386 lib32gcc-5-dev lib32stdc++-5-dev
-  - wget http://security.ubuntu.com/ubuntu/pool/main/g/gcc-5/libstdc++6_5.4.0-6ubuntu1~16.04.10_amd64.deb
-  - mkdir ./libc
-  - dpkg-deb -x ./libstdc++6_5.4.0-6ubuntu1~16.04.10_amd64.deb ./libc
-  - export LD_LIBRARY_PATH=`pwd`/libc/usr/lib/x86_64-linux-gnu/
-  - wget http://releases.llvm.org/6.0.1/clang+llvm-6.0.1-x86_64-linux-gnu-ubuntu-14.04.tar.xz
-  - tar -xf ./clang+llvm-6.0.1-x86_64-linux-gnu-ubuntu-14.04.tar.xz
-  - sudo cp clang+llvm-6.0.1-x86_64-linux-gnu-ubuntu-14.04/bin/clang-format /usr/local/bin/
-  - which clang-format
-  - clang-format --version
 
 install: true
 

Makefile

@@ -332,7 +332,7 @@ install_prerequisites:
 	sudo apt-get install -y -q g++-aarch64-linux-gnu || true
 	sudo apt-get install -y -q g++-powerpc64le-linux-gnu || true
 	sudo apt-get install -y -q g++-arm-linux-gnueabi || true
-	sudo apt-get install -y -q ragel
+	sudo apt-get install -y -q ragel clang-format
 	go get -u golang.org/x/tools/cmd/goyacc
 	go get -u github.com/golangci/golangci-lint/cmd/golangci-lint