Libraries with cross-references between them.

[ronald-cron-arm]

Currently, four libraries are built: tfpsacrypto, builtin, everest, and p256m, with cross-references between them. How these cross-references are handled is linker-dependent, as we observed in #277. Instead, we should build a single crypto library that includes the core, the builtin, and, if necessary, the everest and p256m code.

[gilles-peskine-arm]

One consequence is that shared library builds fail on modern systems (thanks Felix).

…
/usr/bin/ld: ../../drivers/builtin/libbuiltin.so: undefined reference to `psa_asymmetric_encrypt'
/usr/bin/ld: ../../drivers/builtin/libbuiltin.so: undefined reference to `psa_crypto_driver_pake_get_user'
collect2: error: ld returned 1 exit status
make[2]: *** [programs/test/CMakeFiles/which_aes.dir/build.make:101: programs/test/which_aes] Error 1
make[1]: *** [CMakeFiles/Makefile2:1127: programs/test/CMakeFiles/which_aes.dir/all] Error 2