.travis.yml: enable ccache

Travis has `cache: ccache` feature so let us enable it.  Also, because
`config.cache` is generated during the compilation why not cache that
file for a later use.  [fix GH-2013]

Caveats:

- When something went wrong, cache entries can be deleted from
  https://travis-ci.org/ruby/ruby/caches (requires login).

- See `ccache(1)` manual page for the new environment variables.

- `ccache` thinks two compilations are not identical if they produce
  different diagnostics.  The -fno-diagnostics-color option is to
  prevent such cache missihts only because TTY is present / absent at
  the compilation time.

- In this changeset two "ccache --show-stats" invocations are inserted
  before and after the compilation to measure cache hit rates etc.
  Will revisit their outputs once the cache is warmed up.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65731 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

.travis.yml

@@ -55,10 +55,19 @@ addons:
       - libffi
       - openssl@1.1
       - zlib
+      - ccache
+
+cache:
+  ccache: true
+  directories:
+    - "$HOME/config_2nd"
 
 env:
   global:
     - "CONFIGURE_TTY=no"
+    - "CCACHE_COMPILERCHECK=none"
+    - "CCACHE_NOCOMPRESS=1"
+    - "CCACHE_MAXSIZE=512Mi"
 
 .org.ruby-lang.ci.matrix-definitions:
 
@@ -169,8 +178,8 @@ env:
     name: i686-linux
     <<: *linux
     sudo: required
-    compiler: "'gcc-8 -m32'"
     env:
+      - "GCC_FLAGS=-m32"
       - "CONFIG_FLAG='debugflags=-g0'"
       - "SETARCH='setarch i686 --verbose --3gb'"
     addons:
@@ -201,8 +210,9 @@ env:
     name: "-ansi -pedantic"
     <<: *linux
     <<: *make-test-only
-    compiler: "'clang -ansi -Werror=pedantic -pedantic-errors -std=iso9899:1990'"
+    compiler: clang
     env:
+      - "GCC_FLAGS='-ansi -Werror=pedantic -pedantic-errors -std=iso9899:1990'"
       - "CONFIG_FLAG="
       - "JOBS="
     # construct warnflags (using bashism...)
@@ -304,16 +314,34 @@ before_script:
   - "make touch-unicode-files"
   - "make -s $JOBS srcs UNICODE_FILES=."
   - "rm config.status Makefile rbconfig.rb .rbconfig.time"
-  - "mkdir build config_1st config_2nd"
+  - |-
+    if [ -d ~/config_2nd ]; then
+      cp -pr ~/config_2nd build
+    else
+      mkdir build
+    fi
+  - "mkdir config_1st config_2nd"
   - "chmod -R a-w ."
-  - "chmod u+w build config_1st config_2nd"
+  - "chmod -R u+w build config_1st config_2nd"
   - "cd build"
-  - "$SETARCH ../configure -C --disable-install-doc --prefix=/tmp/ruby-prefix --with-gcc=\"$CC\" $CONFIG_FLAG \"${CONFIG_FLAG_ARRAY[@]}\""
+  - "ccache --show-stats"
+  - |-
+    case "$CC" in
+    gcc*)   the_gcc=(ccache $CC ${GCC_FLAGS[@]} -fno-diagnostics-color) ;;
+    clang*) the_gcc=(ccache $CC ${GCC_FLAGS[@]} -fno-color-diagnostics) ;;
+    esac
+    $SETARCH ../configure -C --disable-install-doc --prefix=/tmp/ruby-prefix --with-gcc="${the_gcc[*]}" $CONFIG_FLAG "${CONFIG_FLAG_ARRAY[@]}"
   - "cp -pr config.cache config.status .ext/include ../config_1st"
   - "$SETARCH make reconfig"
   - "cp -pr config.cache config.status .ext/include ../config_2nd"
   - "(cd .. && exec diff -ru config_1st config_2nd)"
+  - |
+    chmod u+w ..
+    rm -r ~/config_2nd
+    mv ../config_2nd ~
+    chmod u-w ..
   - "$SETARCH make -s $JOBS && make install"
+  - "ccache --show-stats"
 
 script:
   - "$SETARCH make -s test TESTOPTS=\"${TESTOPTS=$JOBS -q --tty=no}\""