CI: fixes for clang and asan

[Akim Demaille]

commit 13cdb2d3976813a2512820e536ce181ee7d7efe6
Author: Akim Demaille <address@hidden>
Date:   Wed Sep 26 13:14:32 2018 +0200

    CI: fixes for clang and asan
    
    Bison's test 464 (Syntax error as exception) fails on the CI.
    Do not use clang with asan on Ubuntu's libc++.
    https://bugs.llvm.org/show_bug.cgi?id=17379
    
    * .travis.yml (Clang 7 libc++ and ASAN): New.
    (Clang 6 -O3 and libc++): Really use libc++.
    (Clang 5): Don't use libc++, nor asan (does not work either, same
    reason).

diff --git a/.travis.yml b/.travis.yml
index 8d135c41..4cef8ea6 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -110,23 +110,23 @@ matrix:
     ## Clang.  ##
     ## ------- ##
 
-# Travis is not ready yet for llvm-toolchain-trusty-7.
-#
-#    - name: "Clang 7 ASAN and libc++"
-#      os: linux
-#      addons:
-#        apt:
-#          sources:
-#            - llvm-toolchain-trusty-7
-#            - ubuntu-toolchain-r-test
-#          packages:
-#            - clang-7.0
-#            - libc++-dev
-#            # For llvm-symbolizer.
-#            - llvm-7.0
-#      env:
-#        - MATRIX_EVAL="CC='clang-7.0 -fsanitize=address' CXX='clang++-7.0 
-fsanitize=address -stdlib=libc++'"
-#        - ASAN_SYMBOLIZER_PATH=/usr/lib/llvm-7.0/bin/llvm-symbolizer
+    - name: "Clang 7 libc++ and ASAN"
+      os: linux
+      addons:
+        apt:
+          sources:
+            # Travis is not ready yet:
+            # - llvm-toolchain-trusty-7
+            - sourceline: 'deb http://apt.llvm.org/trusty/ 
llvm-toolchain-trusty-7 main'
+              key_url: 'http://apt.llvm.org/llvm-snapshot.gpg.key'
+            - ubuntu-toolchain-r-test
+          packages:
+            - clang-7
+            - libc++-7-dev
+            - libc++abi-7-dev
+      env:
+        # Do not use ASAN with ubuntu's libc++: 
https://bugs.llvm.org/show_bug.cgi?id=17379
+        - MATRIX_EVAL="CC='clang-7 -fsanitize=address' CXX='clang++-7 
-fsanitize=address -stdlib=libc++'"
 
     - name: "Clang 6 -O3 and libc++"
       os: linux
@@ -139,10 +139,10 @@ matrix:
             - clang-6.0
             - libc++-dev
       env:
-        - MATRIX_EVAL="CC=clang-6.0 && CXX=clang++-6.0"
+        - MATRIX_EVAL="CC=clang-6.0 && CXX='clang++-6.0 -stdlib=libc++'"
         - CONFIGUREFLAGS='CPPFLAGS=-DNDEBUG CFLAGS=-O3 CXXFLAGS=-O3'
 
-    - name: "Clang 5 ASAN"
+    - name: "Clang 5"
       os: linux
       addons:
         apt:
@@ -152,7 +152,7 @@ matrix:
             - clang-5.0
             - libc++-dev
       env:
-        - MATRIX_EVAL="CC='clang-5.0 -fsanitize=address' CXX='clang++-5.0 
-fsanitize=address -stdlib=libc++'"
+        - MATRIX_EVAL="CC='clang-5.0' CXX='clang++-5.0'"
 
     - name: "Clang 4"
       os: linux