Move context verifier to a better place

In terms of CMake, we want it to be part of the mbedtls_test_helpers
object collection, which as the name does not suggest, is actually for
SSL, and not part of mbedtls_test which is generic.

The easiest way to achieve that is to move the source file to
test_helpers which again as the name does not reflect is for SSL.

Then we just need ssl_server2 and ssl_client2 to link to
mbedtls_test_helpers.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>

programs/ssl/CMakeLists.txt

@@ -34,6 +34,7 @@ foreach(exe IN LISTS executables)
     set(extra_sources "")
     if(exe STREQUAL "ssl_client2" OR exe STREQUAL "ssl_server2")
         list(APPEND extra_sources
+            $<TARGET_OBJECTS:mbedtls_test_helpers>
             ssl_test_lib.c
             ${MBEDTLS_FRAMEWORK_DIR}/tests/programs/query_config.h
             ${CMAKE_CURRENT_BINARY_DIR}/../test/query_config.c)