Use system clang for Linux ANGLE builds

scripts/build-linux-static-graphics.sh

@@ -168,6 +168,8 @@ target_cpu = "$TARGET_CPU"
 is_debug = false
 is_component_build = false
 is_clang = true
+clang_base_path = "/usr"
+clang_use_chrome_plugins = false
 use_custom_libcxx = false
 use_sysroot = false
 use_lld = false