CI: sort the matrix in reverse-chronological

[Akim Demaille]

commit 0e38617ad773a15444674e8a1d959c2f69995490
Author: Akim Demaille <address@hidden>
Date:   Sun Sep 9 17:38:30 2018 +0200

    CI: sort the matrix in reverse-chronological
    
    There are only three builds at a time: show the result of modern
    compilers first.
    
    * .travis.yml (matrix): Sort in reverse-chronological.

diff --git a/.travis.yml b/.travis.yml
index c49b9dac..c228c63f 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,16 +2,18 @@ language: cpp
 
 matrix:
   include:
-    # GCC.
+    ## ----- ##
+    ## GCC.  ##
+    ## ----- ##
     - os: linux
       addons:
         apt:
           sources:
             - ubuntu-toolchain-r-test
           packages:
-            - g++-4.6
+            - g++-8
       env:
-         - MATRIX_EVAL="CC=gcc-4.6 && CXX=g++-4.6"
+        - MATRIX_EVAL="CC=gcc-8 && CXX=g++-8"
 
     - os: linux
       addons:
@@ -19,9 +21,9 @@ matrix:
           sources:
             - ubuntu-toolchain-r-test
           packages:
-            - g++-4.9
+            - g++-7
       env:
-         - MATRIX_EVAL="CC=gcc-4.9 && CXX=g++-4.9"
+        - MATRIX_EVAL="CC=gcc-7 && CXX=g++-7 && CPPFLAGS=-DNDEBUG && 
CFLAGS=-O3 && CXXFLAGS=-O3"
 
     - os: linux
       addons:
@@ -29,9 +31,9 @@ matrix:
           sources:
             - ubuntu-toolchain-r-test
           packages:
-            - g++-5
+            - g++-6
       env:
-         - MATRIX_EVAL="CC=gcc-5 && CXX=g++-5"
+        - MATRIX_EVAL="CC=gcc-6 && CXX=g++-6"
 
     - os: linux
       addons:
@@ -39,9 +41,9 @@ matrix:
           sources:
             - ubuntu-toolchain-r-test
           packages:
-            - g++-6
+            - g++-5
       env:
-        - MATRIX_EVAL="CC=gcc-6 && CXX=g++-6"
+         - MATRIX_EVAL="CC=gcc-5 && CXX=g++-5"
 
     - os: linux
       addons:
@@ -49,9 +51,9 @@ matrix:
           sources:
             - ubuntu-toolchain-r-test
           packages:
-            - g++-7
+            - g++-4.9
       env:
-        - MATRIX_EVAL="CC=gcc-7 && CXX=g++-7 && CPPFLAGS=-DNDEBUG && 
CFLAGS=-O3 && CXXFLAGS=-O3"
+         - MATRIX_EVAL="CC=gcc-4.9 && CXX=g++-4.9"
 
     - os: linux
       addons:
@@ -59,50 +61,53 @@ matrix:
           sources:
             - ubuntu-toolchain-r-test
           packages:
-            - g++-8
+            - g++-4.6
       env:
-        - MATRIX_EVAL="CC=gcc-8 && CXX=g++-8"
+         - MATRIX_EVAL="CC=gcc-4.6 && CXX=g++-4.6"
 
-    # Clang.
+    ## ------- ##
+    ## Clang.  ##
+    ## ------- ##
     - os: linux
       addons:
         apt:
+          sources:
+            - llvm-toolchain-trusty-5.0
           packages:
-            - clang-3.3
+            - clang-5.0
       env:
-        # No versioned name installed.
-        - MATRIX_EVAL="CC=clang && CXX=clang++"
+        - MATRIX_EVAL="CC=clang-5.0 && CXX=clang++-5.0 && CPPFLAGS=-DNDEBUG && 
CFLAGS=-O3 && CXXFLAGS=-O3"
 
     - os: linux
       addons:
         apt:
+          sources:
+            - llvm-toolchain-trusty-4.0
           packages:
-            - clang-3.4
+            - clang-4.0
       env:
-        # No versioned name installed.
-        - MATRIX_EVAL="CC=clang && CXX=clang++"
+        - MATRIX_EVAL="CC=clang-4.0 && CXX=clang++-4.0"
 
     - os: linux
       addons:
         apt:
           sources:
-            - ubuntu-toolchain-r-test
-            - llvm-toolchain-precise-3.5
+            - llvm-toolchain-trusty-3.9
           packages:
-            - clang-3.5
+            - clang-3.9
       env:
-        - MATRIX_EVAL="CC=clang-3.5 && CXX=clang++-3.5"
+        - MATRIX_EVAL="CC=clang-3.9 && CXX=clang++-3.9"
 
     - os: linux
       addons:
         apt:
           sources:
             - ubuntu-toolchain-r-test
-            - llvm-toolchain-precise-3.6
+            - llvm-toolchain-precise-3.8
           packages:
-            - clang-3.6
+            - clang-3.8
       env:
-        - MATRIX_EVAL="CC=clang-3.6 && CXX=clang++-3.6"
+        - MATRIX_EVAL="CC=clang-3.8 && CXX=clang++-3.8"
 
     - os: linux
       addons:
@@ -120,41 +125,40 @@ matrix:
         apt:
           sources:
             - ubuntu-toolchain-r-test
-            - llvm-toolchain-precise-3.8
+            - llvm-toolchain-precise-3.6
           packages:
-            - clang-3.8
+            - clang-3.6
       env:
-        - MATRIX_EVAL="CC=clang-3.8 && CXX=clang++-3.8"
+        - MATRIX_EVAL="CC=clang-3.6 && CXX=clang++-3.6"
 
     - os: linux
       addons:
         apt:
           sources:
-            - llvm-toolchain-trusty-3.9
+            - ubuntu-toolchain-r-test
+            - llvm-toolchain-precise-3.5
           packages:
-            - clang-3.9
+            - clang-3.5
       env:
-        - MATRIX_EVAL="CC=clang-3.9 && CXX=clang++-3.9"
+        - MATRIX_EVAL="CC=clang-3.5 && CXX=clang++-3.5"
 
     - os: linux
       addons:
         apt:
-          sources:
-            - llvm-toolchain-trusty-4.0
           packages:
-            - clang-4.0
+            - clang-3.4
       env:
-        - MATRIX_EVAL="CC=clang-4.0 && CXX=clang++-4.0"
+        # No versioned name installed.
+        - MATRIX_EVAL="CC=clang && CXX=clang++"
 
     - os: linux
       addons:
         apt:
-          sources:
-            - llvm-toolchain-trusty-5.0
           packages:
-            - clang-5.0
+            - clang-3.3
       env:
-        - MATRIX_EVAL="CC=clang-5.0 && CXX=clang++-5.0 && CPPFLAGS=-DNDEBUG && 
CFLAGS=-O3 && CXXFLAGS=-O3"
+        # No versioned name installed.
+        - MATRIX_EVAL="CC=clang && CXX=clang++"
 
 before_install:
   - sudo apt-get update -qq