Bug 1467658 - Build toolchains with clang 6 instead of 3.9. r=chmanchester

For those toolchains built with clang, use clang 6.

The only jobs remaining to use the clang 3.9 toolchain are the
base-toolchains build jobs.

--HG--
extra : rebase_source : 1fe92e9e2730c11ce5ce87dddd6496228c3d270c

taskcluster/ci/toolchain/linux.yml

@@ -298,7 +298,7 @@ linux64-cctools-port:
             - 'taskcluster/scripts/misc/tooltool-download.sh'
         toolchain-artifact: public/build/cctools.tar.xz
     toolchains:
-        - linux64-clang-3.9
+        - linux64-clang-6
 
 linux64-hfsplus:
     description: "hfsplus toolchain build"
@@ -318,7 +318,7 @@ linux64-hfsplus:
             - 'taskcluster/scripts/misc/tooltool-download.sh'
         toolchain-artifact: public/build/hfsplus-tools.tar.xz
     toolchains:
-        - linux64-clang-3.9
+        - linux64-clang-6
 
 linux64-libdmg:
     description: "libdmg-hfsplus toolchain build"

taskcluster/ci/toolchain/macosx.yml

@@ -32,7 +32,7 @@ macosx64-clang:
         toolchain-artifact: public/build/clang.tar.xz
     toolchains:
         - linux64-cctools-port
-        - linux64-clang-3.9
+        - linux64-clang-6
         - linux64-gcc-4.9
 
 macosx64-clang-tidy:
@@ -62,7 +62,7 @@ macosx64-clang-tidy:
         toolchain-artifact: public/build/clang-tidy.tar.xz
     toolchains:
         - linux64-cctools-port
-        - linux64-clang-3.9
+        - linux64-clang-6
         - linux64-gcc-4.9
 
 macosx64-cctools-port:
@@ -86,7 +86,7 @@ macosx64-cctools-port:
         toolchain-artifact: public/build/cctools.tar.bz2
     toolchains:
         - linux64-cctools-port
-        - linux64-clang-3.9
+        - linux64-clang-6
 
 macosx64-gn:
     description: "gn toolchain build"
@@ -110,4 +110,4 @@ macosx64-gn:
         toolchain-artifact: public/build/gn.tar.xz
     toolchains:
         - linux64-cctools-port
-        - linux64-clang-3.9
+        - linux64-clang-6