travis.yml: Use clang++ in the Clang tests

Our configure script does not look for clang++ automatically, so we
should use --cxx=clang++ to make sure that we test our C++ code with
Clang, too. And while we're at it, also use --host-cc=clang here
to avoid that we use the normal "cc" as host C compiler.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200518083316.25065-1-thuth@redhat.com>
Message-Id: <20200520140541.30256-4-alex.bennee@linaro.org>

.travis.yml

@@ -205,14 +205,15 @@ jobs:
     # Test with Clang for compile portability (Travis uses clang-5.0)
     - name: "Clang (user)"
       env:
-        - CONFIG="--disable-system"
+        - CONFIG="--disable-system --host-cc=clang --cxx=clang++"
         - CACHE_NAME="${TRAVIS_BRANCH}-linux-clang-default"
       compiler: clang
 
 
     - name: "Clang (main-softmmu)"
       env:
-        - CONFIG="--target-list=${MAIN_SOFTMMU_TARGETS} "
+        - CONFIG="--target-list=${MAIN_SOFTMMU_TARGETS}
+                  --host-cc=clang --cxx=clang++"
         - CACHE_NAME="${TRAVIS_BRANCH}-linux-clang-sanitize"
       compiler: clang
       before_script:
@@ -222,7 +223,8 @@ jobs:
 
     - name: "Clang (other-softmmu)"
       env:
-        - CONFIG="--disable-user --target-list-exclude=${MAIN_SOFTMMU_TARGETS}"
+        - CONFIG="--disable-user --target-list-exclude=${MAIN_SOFTMMU_TARGETS}
+                  --host-cc=clang --cxx=clang++"
         - CACHE_NAME="${TRAVIS_BRANCH}-linux-clang-default"
       compiler: clang