The function mbedtls_test_hook_error_add() is declared in the library
but supplied by test helpers in framework/tests/src, so it is undefined
in library-only builds. This messes up our checks for missing symbols,
so disable MBEDTLS_TEST_HOOKS when we are building to check missing
symbols.
Signed-off-by: David Horstmann <david.horstmann@arm.com>