Fix CMakeList.txt for counters test renaming
diff --git a/CMakeLists.txt b/CMakeLists.txt
index bae57cd..178acc6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1995,7 +1995,7 @@
 
   add_executable(ftrace_helper src/ftrace/ftrace_helper.c)
   if (x86ish AND rr_64BIT)
-    add_executable(counters src/counters-test/counters.c)
+    add_executable(counters src/counters-test/counters.cc)
   endif()
 endif()