Unable to build the test framework when no SHA2 hash module is enabled

[gilles-peskine-arm]

With Mbed TLS 2.27 or 3.0:

echo '#define MBEDTLS_AES_C' >include/mbedtls/mbedtls_config.h # config.h on 2.2x
make

Expected outcome: the build succeeds.

Actual outcome:

…
In file included from src/random.c:38:
../include/mbedtls/entropy.h:129:5: error: unknown type name ‘mbedtls_sha256_context’
  129 |     mbedtls_sha256_context  accumulator;
      |     ^~~~~~~~~~~~~~~~~~~~~~
make[1]: *** [Makefile:97: src/random.o] Error 1
make: *** [Makefile:23: mbedtls_test] Error 2

This is admittedly an exotic configuration (there are few useful library configurations that don't include SHA-256 or SHA-512, even in builds without the entropy module, which are themselves somewhat unusual). But it does make sense if you only want symmetric cryptography with pre-generated keys. And it will become less exotic once SHA-3 is added.

[tom-cosgrove-arm]

Closing this as fixed by #5269 for development and #5167 for 2.x.

I've confirmed that both branches build with no errors given the one-line config in the description