.travis.yml: Cache Linux/Clang jobs together

These jobs build different components but use the same
host features. Put them in the same cache bucket.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

.travis.yml

@@ -173,11 +173,13 @@ matrix:
     # Test with Clang for compile portability (Travis uses clang-5.0)
     - env:
         - CONFIG="--disable-system"
+        - CACHE_NAME="${TRAVIS_BRANCH}-linux-clang-default"
       compiler: clang
 
 
     - env:
         - CONFIG="--disable-user --target-list=${MAIN_SOFTMMU_TARGETS}"
+        - CACHE_NAME="${TRAVIS_BRANCH}-linux-clang-default"
       compiler: clang
 
 
@@ -190,6 +192,7 @@ matrix:
 
     - env:
         - CONFIG="--disable-user --target-list-exclude=${MAIN_SOFTMMU_TARGETS}"
+        - CACHE_NAME="${TRAVIS_BRANCH}-linux-clang-default"
       compiler: clang