When building with CMake, for sample programs that only use
functionality in libmbedcrypto (i.e. crypto and platform), link with
libmbedcrypto, not with libmbedtls.
This doesn't change the result, because the linker skips libraries in
which no symbol is used, but it changes the build dependencies, and it
has the advantage of bringing programs/*/CMakeLists.txt closer to the
corresponding files under crypto/.
The programs concerned are crypto sample and test programs, and
programs that only use (potential) platform functions such as
mbedtls_printf. dh_client and dh_server keep linking with mbedtls
because they use functions from the net_sockets module.
