Travis: restore clang with trusty & included clang

Upgraded to using Tavis trusty dist (from precise)

Ubuntu's clang is only 3.4 though.

For fancy address, thread-sanitizer stuff, easier to do on OS X.
We can use the clang that comes with xcode 8 beta.

.travis.yml

@@ -13,31 +13,27 @@ matrix:
             - expect
             - gettext
             - libncurses5-dev
-
     - os: linux
       compiler: clang
       addons:
         apt:
-          sources:
-            - llvm-toolchain-precise-3.8
-            - ubuntu-toolchain-r-test
           packages:
-            - clang-3.8
-            - llvm-3.8 # for llvm-symbolizer
             - bc
             - expect
             - gettext
             - libncurses5-dev
         env:
-        - CXXFLAGS="-g -fno-omit-frame-pointer -fsanitize=address"
-        - ASAN_OPTIONS=check_initialization_order=1:detect_stack_use_after_return=1:detect_leaks=1
-      before_install: export CXX=clang++-3.8
-
+          - CXXFLAGS="-g -fno-omit-frame-pointer"
     - os: osx
+      osx_image: xcode8
       before_install:
         - brew update
-        - brew install pcre2 # use system PCRE2
-
+        - brew outdated pcre2 || brew upgrade pcre2 # use system PCRE2
+        - brew outdated xctool || brew upgrade xctool # for xcode... soon.
+      addons:
+        env:
+          - CXXFLAGS="-g -fno-omit-frame-pointer -fsanitize=address -lstdc++"
+          - ASAN_OPTIONS=check_initialization_order=1:detect_stack_use_after_return=1:detect_leaks=1
   fast_finish: true
 
 script: