'+crypto' means '+aes' and '+sha2' for arch >= ARMv8 when they were
not disabled explicitly. But this is correctly handled only in case of
'-march' option, though the feature may also be specified through
the '-mcpu' or '-mfpu' options. In the following example:
$ clang -mcpu=cortex-a57 -mfpu=crypto-neon-fp-armv8
'aes' and 'sha2' are disabled that is quite unexpected:
$ clang -cc1 -triple armv8--- -target-cpu cortex-a57 <...> -target-feature -sha2 -target-feature -aes -target-feature +crypto
This exposed by https://reviews.llvm.org/D63936 that makes
the 'aes' and 'sha2' features disabled by default.
So, while handling the 'crypto' feature we need to take into account:
- a CPU name, as it provides the information about architecture (if no '-march' option specified),
- features, specified by the '-mcpu' and '-mfpu' options.