Tweak configuration of `tools/test.py`'s fast mode.

Change-Id: Idbf424da0ddeb817aa089cf78814ab9dfb542ebf
diff --git a/tools/config.py b/tools/config.py
index 474c853..dd8cff7 100644
--- a/tools/config.py
+++ b/tools/config.py
@@ -43,6 +43,6 @@
 # The list of C++ standard to test for.
 tested_cpp_standards = ['c++98', 'c++11']
 # The list of compilers tested.
-tested_compilers = ['g++', 'clang++']
+tested_compilers = ['clang++', 'g++']