Update Travis comments

.travis.yml

@@ -433,6 +433,11 @@ jobs:
         - BUILD_OS=linux
         - BUILD_MODE=all
         - BUILD_JOBS=2
+      addons:
+        apt:
+          packages: ['clang-6.0', 'clang++-6.0']
+          sources: &sources
+            - llvm-toolchain-bionic-6.0
     - os: linux
       name: Android on Linux (armeabi-v7a)
       arch: amd64
@@ -568,12 +573,8 @@ jobs:
         - BUILD_ARCH=iPhoneSimulator
     # We should be OK with PPC64 and GCC until Travis disallows
     # access to the build machines. Clang is a differnt story.
-    # The LLVM devs have their heads so far up their ass I don't
-    # think we can un-fuck the mess they created on PowerPC. The
-    # LLVM devs appear to have given up and define everything
-    # from all the compilers to all the features. It does not
-    # seem to matter to them the compiler does not actually
-    # support what LLVM is advertising in the preprocessor.
+    # Clang 7.0 and below will likely have trouble due to
+    # https://bugs.llvm.org/show_bug.cgi?id=39704
     - os: linux
       name: Linux with GCC (all)
       arch: ppc64le