Disable bundled clang compiler build.

v8pp/build-v8.sh

 echo "v8_use_external_startup_data = false" | tee -a out/x64.release/args.gn
 echo "v8_use_snapshot = false"              | tee -a out/x64.release/args.gn
 echo "use_custom_libcxx = false"            | tee -a out/x64.release/args.gn
+# possibly they use a different version of clang compiling v8.
+# however, I already set my own, probably newer clang version.
+# ran into: https://groups.google.com/forum/#!topic/v8-users/Jb1VSouy2Z0
+echo "is_clang = false"                     | tee -a out/x64.release/args.gn
+
 
 # produce monolith (single static all in one .a file)
 echo "v8_monolithic = true"                 | tee -a out/x64.release/args.gn