Enable ccache on Travis, plus travis.yml restructuring

All jobs now have ccache enabled, which means that subsequent compilation should be able to reuse the compiled files, and thus the job running time should be faster.

As part of the above, travis.yml needed to be restructured, in particular:
* instead of running the compilation and tests as one command, they are split
* cegis etc. compilation takes place before the tests are run.

Author: forejtv

.travis.yml

@@ -7,30 +7,44 @@ matrix:
     - os: linux
       sudo: required
       compiler: gcc
+      cache: ccache
       services:
         - docker
       before_install:
         - docker pull diffblue/cbmc-builder:alpine
       env:
-        - PRE_COMMAND="docker run -v ${TRAVIS_BUILD_DIR}:/cbmc diffblue/cbmc-builder:alpine"
-        - COMPILER=g++
+        - PRE_COMMAND="docker run -v ${TRAVIS_BUILD_DIR}:/cbmc -v ${HOME}/.ccache:/root/.ccache diffblue/cbmc-builder:alpine"
+        - COMPILER="ccache g++"
 
     # OS X using g++
     - os: osx
       sudo: false
       compiler: gcc
+      cache: ccache
+      before_install:
+          #we create symlink to non-ccache gcc, to be used in tests
+        - mkdir bin ; ln -s /usr/bin/gcc bin/gcc
+        - brew install ccache
+        - export PATH=/usr/local/opt/ccache/libexec:$PATH
       env: COMPILER=g++
 
     # OS X using clang++
     - os: osx
       sudo: false
       compiler: clang
-      env: COMPILER=clang++
+      cache: ccache
+      before_install:
+        - brew install ccache
+        - export PATH=/usr/local/opt/ccache/libexec:$PATH
+      env:
+        - COMPILER="ccache clang++ -Qunused-arguments -fcolor-diagnostics"
+        - CCACHE_CPP2=yes
 
     # Ubuntu Linux with glibc using g++-5
     - os: linux
       sudo: false
       compiler: gcc
+      cache: ccache
       addons:
         apt:
           sources:
@@ -42,12 +56,13 @@ matrix:
       before_install:
         - mkdir bin ; ln -s /usr/bin/gcc-5 bin/gcc
       # env: COMPILER=g++-5 SAN_FLAGS="-fsanitize=undefined -fno-sanitize-recover -fno-omit-frame-pointer"
-      env: COMPILER=g++-5
+      env: COMPILER="g++-5"
 
     # Ubuntu Linux with glibc using clang++-3.7
     - os: linux
       sudo: false
       compiler: clang
+      cache: ccache
       addons:
         apt:
           sources:
@@ -60,23 +75,33 @@ matrix:
             - libubsan0
       before_install:
         - mkdir bin ; ln -s /usr/bin/clang-3.7 bin/gcc
+        - export CCACHE_CPP2=yes
       # env: COMPILER=clang++-3.7 SAN_FLAGS="-fsanitize=undefined -fno-sanitize-recover=undefined,integer -fno-omit-frame-pointer"
-      env: COMPILER=clang++-3.7
+      env:
+        - COMPILER="ccache clang++-3.7 -Qunused-arguments -fcolor-diagnostics"
+        - CCACHE_CPP2=yes
 
     - env: NAME="CPP-LINT"
-      script: scripts/travis_lint.sh || true
+      install:
+      script: scripts/travis_lint.sh
+      before_cache:
+
+install:
+  - COMMAND="make -C src minisat2-download" &&
+    eval ${PRE_COMMAND} ${COMMAND}
+  - COMMAND="make -C src CXX=\"$COMPILER\" CXXFLAGS=\"-Wall -O2 -g -Werror -Wno-deprecated-register -pedantic -Wno-sign-compare\" -j2" &&
+    eval ${PRE_COMMAND} ${COMMAND}
+  - COMMAND="make -C src CXX=\"$COMPILER\" CXXFLAGS=$FLAGS -j2 cegis.dir clobber.dir memory-models.dir musketeer.dir" &&
+    eval ${PRE_COMMAND} ${COMMAND}
+  - COMMAND="make -C src clean" &&
+    eval ${PRE_COMMAND} ${COMMAND}
+  - COMMAND="make -C src CXX=$COMPILER CXXFLAGS=\"-Wall -O0 -ggdb3 -Werror -Wno-deprecated-register -pedantic -Wno-sign-compare -DDEBUG\" -j2" &&
+    eval ${PRE_COMMAND} ${COMMAND}
 
 script:
-  - if [ -L bin/gcc ] ; then export PATH=$PWD/bin:$PATH ; fi ;
-    COMMAND="make -C src minisat2-download" &&
-    eval ${PRE_COMMAND} ${COMMAND} &&
-    COMMAND="make -C src CXX=$COMPILER CXXFLAGS=\"-Wall -O2 -g -Werror -Wno-deprecated-register -pedantic -Wno-sign-compare\" -j2" &&
-    eval ${PRE_COMMAND} ${COMMAND} &&
+  - if [ -e bin/gcc ] ; then export PATH=$PWD/bin:$PATH ; fi ;
     COMMAND="env UBSAN_OPTIONS=print_stacktrace=1 make -C regression test" &&
-    eval ${PRE_COMMAND} ${COMMAND} &&
-    COMMAND="make -C src CXX=$COMPILER CXXFLAGS=$FLAGS -j2 cegis.dir clobber.dir memory-models.dir musketeer.dir" &&
-    eval ${PRE_COMMAND} ${COMMAND} &&
-    COMMAND="make -C src clean" &&
-    eval ${PRE_COMMAND} ${COMMAND} &&
-    COMMAND="make -C src CXX=$COMPILER CXXFLAGS=\"-Wall -O0 -ggdb3 -Werror -Wno-deprecated-register -pedantic -Wno-sign-compare -DDEBUG\" -j2" &&
     eval ${PRE_COMMAND} ${COMMAND}
+
+before_cache:
+  - ccache -s