misc: switch to clang-9

Type: improvement
Change-Id: Iebf77a63c0c19b130a3fbd26b5293304a9fed4c1
Signed-off-by: Damjan Marion <damarion@cisco.com>
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 89b4b96..16ae7d5 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -13,6 +13,8 @@
 
 cmake_minimum_required(VERSION 3.5 FATAL_ERROR)
 
+set(CMAKE_C_COMPILER_NAMES clang-9 cc)
+
 project(vpp C)
 
 include(CheckCCompilerFlag)