fix Issue 12554 - [ICE](struct.c line 898) with failed delegate purity
add semantics for @nogc
Merge pull request #3490 from WalterBright/more-nogc

DIP60: add semantics for @nogc
small refactor
Merge pull request #3494 from WalterBright/refactor-isNogc

small refactor
fix Issue 12630 - @nogc should recognize compile-time evaluation context
Fix Issue 11620 - Emit enum member values to json output.
Merge pull request #3472 from AndrejMitrovic/Fix11620

Issue 11620 - Emit enum member values to json output.
Merge pull request #3493 from 9rnsr/fix12630

Issue 12630 - @nogc should recognize compile-time evaluation context
Merge pull request #3492 from 9rnsr/fix12554

[REG2.066a] Issue 12554 - [ICE](struct.c line 898) with failed delegate purity