Add generated files

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8d27a82..8d3f08a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -59,7 +59,7 @@
 if(CMAKE_HOST_WIN32)
     option(GEN_FILES "Generate the auto-generated files as needed" OFF)
 else()
-    option(GEN_FILES "Generate the auto-generated files as needed" ON)
+    option(GEN_FILES "Generate the auto-generated files as needed" OFF)
 endif()
 
 option(DISABLE_PACKAGE_CONFIG_AND_INSTALL "Disable package configuration, target export and installation" ${MBEDTLS_AS_SUBPROJECT})