CI: Clang 6.0 is not available

[Akim Demaille]

commit 4ed85690eb8c4e360535665d3d48e159a9f19e26
Author: Akim Demaille <akim.demai...@gmail.com>
Date:   Sun Sep 9 09:34:43 2018 +0200

    CI: Clang 6.0 is not available
    
    But Clang 3.3 is.
    
    * .travis.yml (addons): Remove, it appears to be ignore if the matrix
    also defines it.
    (matrix): Update.

diff --git a/.travis.yml b/.travis.yml
index 0982358b..80a6603f 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,13 +1,18 @@
 language: cpp
 
-addons:
-  apt:
-    packages:
-      - ccache
-
 matrix:
   include:
-    # works on Precise and Trusty
+    # GCC.
+    - os: linux
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            - g++-4.6
+      env:
+         - MATRIX_EVAL="CC=gcc-4.6 && CXX=g++-4.6"
+
     - os: linux
       addons:
         apt:
@@ -18,7 +23,6 @@ matrix:
       env:
          - MATRIX_EVAL="CC=gcc-4.9 && CXX=g++-4.9"
 
-    # works on Precise and Trusty
     - os: linux
       addons:
         apt:
@@ -29,7 +33,6 @@ matrix:
       env:
          - MATRIX_EVAL="CC=gcc-5 && CXX=g++-5"
 
-    # works on Precise and Trusty
     - os: linux
       addons:
         apt:
@@ -40,7 +43,6 @@ matrix:
       env:
         - MATRIX_EVAL="CC=gcc-6 && CXX=g++-6"
 
-    # works on Precise and Trusty
     - os: linux
       addons:
         apt:
@@ -51,7 +53,6 @@ matrix:
       env:
         - MATRIX_EVAL="CC=gcc-7 && CXX=g++-7 && CPPFLAGS=-DNDEBUG && 
CFLAGS=-O3 && CXXFLAGS=-O3"
 
-    # works on Precise and Trusty
     - os: linux
       addons:
         apt:
@@ -62,19 +63,26 @@ matrix:
       env:
         - MATRIX_EVAL="CC=gcc-8 && CXX=g++-8"
 
-    # works on Precise and Trusty
+    # Clang.
+    - os: linux
+      addons:
+        apt:
+          packages:
+            - clang-3.3
+      env:
+        - MATRIX_EVAL="CC=clang-3.3 && CXX=clang++-3.3"
+
     - os: linux
       addons:
         apt:
           sources:
             - ubuntu-toolchain-r-test
-            - llvm-toolchain-precise-3.4
+            - llvm-toolchain-precise-3.5
           packages:
-            - clang-3.4
+            - clang-3.5
       env:
-        - MATRIX_EVAL="CC=clang-3.4 && CXX=clang++-3.4"
+        - MATRIX_EVAL="CC=clang-3.5 && CXX=clang++-3.5"
 
-    # works on Precise and Trusty
     - os: linux
       addons:
         apt:
@@ -86,7 +94,6 @@ matrix:
       env:
         - MATRIX_EVAL="CC=clang-3.6 && CXX=clang++-3.6"
 
-    # works on Precise and Trusty
     - os: linux
       addons:
         apt:
@@ -98,7 +105,6 @@ matrix:
       env:
         - MATRIX_EVAL="CC=clang-3.7 && CXX=clang++-3.7"
 
-    # works on Precise and Trusty
     - os: linux
       addons:
         apt:
@@ -110,7 +116,6 @@ matrix:
       env:
         - MATRIX_EVAL="CC=clang-3.8 && CXX=clang++-3.8"
 
-    # works on Trusty
     - os: linux
       addons:
         apt:
@@ -121,7 +126,6 @@ matrix:
       env:
         - MATRIX_EVAL="CC=clang-3.9 && CXX=clang++-3.9"
 
-    # works on Trusty
     - os: linux
       addons:
         apt:
@@ -132,7 +136,6 @@ matrix:
       env:
         - MATRIX_EVAL="CC=clang-4.0 && CXX=clang++-4.0"
 
-    # works on Trusty
     - os: linux
       addons:
         apt:
@@ -143,17 +146,6 @@ matrix:
       env:
         - MATRIX_EVAL="CC=clang-5.0 && CXX=clang++-5.0 && CPPFLAGS=-DNDEBUG && 
CFLAGS=-O3 && CXXFLAGS=-O3"
 
-    # works on Trusty
-    - os: linux
-      addons:
-        apt:
-          sources:
-            - llvm-toolchain-trusty-6.0
-          packages:
-            - clang-6.0
-      env:
-        - MATRIX_EVAL="CC=clang-6.0 && CXX=clang++-6.0"
-
 before_install:
   - sudo apt-get update -qq
   - sudo apt-get install -qq autoconf automake autopoint flex gettext graphviz 
help2man m4 texinfo valgrind