add support for building for the roborio with clang

Change-Id: I1513da14b46f7d1cbe1444c60c810f352ee494ca
diff --git a/aos/build/build.py b/aos/build/build.py
index 90028ba..21e0379 100755
--- a/aos/build/build.py
+++ b/aos/build/build.py
@@ -512,7 +512,7 @@
       return r
 
   ARCHITECTURES = ('arm', 'amd64')
-  COMPILERS = ('clang', 'gcc_frc')
+  COMPILERS = ('clang', 'gcc_frc', 'clang_frc')
   SANITIZERS = ('address', 'undefined', 'integer', 'memory', 'thread', 'none')
   SANITIZER_TEST_WARNINGS = {
       'memory': (True,