CI: Fix/improve Travis cache handling [skip appveyor] #10422

Via https://github.com/neovim/neovim/pull/10412

* use list, no indirection
* use job names
* __FOR_TRAVIS_CACHE__ (more descriptive)

.travis.yml

@@ -47,46 +47,74 @@ env:
     - CCACHE_SLOPPINESS=time_macros,file_macro
     - CCACHE_BASEDIR="$TRAVIS_BUILD_DIR"
 
+anchors:
+  envs: &common-job-env
+    # Do not fall back to cache for "master" for PR on "release" branch:
+    # adds the target branch to the cache key.
+    __FOR_TRAVIS_CACHE__=$TRAVIS_BRANCH
+
 jobs:
   include:
     - stage: normal builds
+      name: clang-asan
       os: linux
       compiler: clang-4.0
       # Use Lua so that ASAN can test our embedded Lua support. 8fec4d53d0f6
-      env: >
-        CLANG_SANITIZER=ASAN_UBSAN
-        CMAKE_FLAGS="$CMAKE_FLAGS -DPREFER_LUA=ON"
-        ASAN_SYMBOLIZE=asan_symbolize-4.0
-    - os: linux
+      env:
+        - CLANG_SANITIZER=ASAN_UBSAN
+        - CMAKE_FLAGS="$CMAKE_FLAGS -DPREFER_LUA=ON"
+        - ASAN_SYMBOLIZE=asan_symbolize-4.0
+        - *common-job-env
+    - name: gcc-functionaltest-lua
+      os: linux
       compiler: gcc
-      env: >
-        FUNCTIONALTEST=functionaltest-lua
-        CMAKE_FLAGS="$CMAKE_FLAGS -DPREFER_LUA=ON"
-        DEPS_CMAKE_FLAGS="$DEPS_CMAKE_FLAGS -DUSE_BUNDLED_LUAJIT=OFF"
-    - os: linux
+      env:
+        - FUNCTIONALTEST=functionaltest-lua
+        - CMAKE_FLAGS="$CMAKE_FLAGS -DPREFER_LUA=ON"
+        - DEPS_CMAKE_FLAGS="$DEPS_CMAKE_FLAGS -DUSE_BUNDLED_LUAJIT=OFF"
+        - *common-job-env
+    - name: gcc-32bit
+      os: linux
       # Travis creates a cache per compiler. Set a different value here to
       # store 32-bit dependencies in a separate cache.
       compiler: gcc
-      env: BUILD_32BIT=ON
-    - os: osx
+      env:
+        - BUILD_32BIT: ON
+        - *common-job-env
+    - name: "OSX: clang"
+      os: osx
       compiler: clang
       osx_image: xcode9.4  # macOS 10.13
-    - os: osx
+      env: *common-job-env
+    - name: "OSX: gcc"
+      os: osx
       compiler: gcc
       osx_image: xcode9.4  # macOS 10.13
+      env: *common-job-env
     - if: branch = master
+      name: lint
       os: linux
-      env: CI_TARGET=lint
+      env:
+        - CI_TARGET=lint
+        - *common-job-env
+
     - stage: Flaky builds
+      name: gcc-coverage
       os: linux
       compiler: gcc
-      env: GCOV=gcov CMAKE_FLAGS="$CMAKE_FLAGS -DUSE_GCOV=ON"
+      env:
+        - GCOV=gcov
+        - CMAKE_FLAGS="$CMAKE_FLAGS -DUSE_GCOV=ON"
+        - *common-job-env
     - os: linux
+      name: clang-tsan
       compiler: clang
-      env: CLANG_SANITIZER=TSAN
+      env:
+        - CLANG_SANITIZER=TSAN
+        - *common-job-env
   allow_failures:
-    - env: GCOV=gcov CMAKE_FLAGS="$CMAKE_FLAGS -DUSE_GCOV=ON"
-    - env: CLANG_SANITIZER=TSAN
+    - name: gcc-coverage
+    - name: clang-tsan
   fast_finish: true
 
 before_install: ci/before_install.sh