Rename project in CMake

TODO: to create symlinks to the old names!
diff --git a/programs/x509/CMakeLists.txt b/programs/x509/CMakeLists.txt
index fe46da5..4e39e45 100644
--- a/programs/x509/CMakeLists.txt
+++ b/programs/x509/CMakeLists.txt
@@ -1,5 +1,5 @@
 set(libs
-     polarssl
+     mbedtls
 )
 
 if(USE_PKCS11_HELPER_LIBRARY)