add core.checkedint
GC: remove redundant null checks.
Merge pull request #839 from WalterBright/checkedint

add core.checkedint
add reference
Merge pull request #846 from WalterBright/add-ref

add reference
Merge pull request #845 from Safety0ff/removeuseless

GC: remove redundant null checks.
Replace use of the deprecated Duration.fracSec with Duration.split.
Merge pull request #848 from jmdavis/semaphore

Replace use of the deprecated Duration.fracSec with Duration.split.
Add `@nogc` to `TypeInfo` and AA functions.
Merge pull request #840 from denis-sh/add-`@nogc`-to-`TypeInfo`-and-AA-functions

Add `@nogc` to `TypeInfo` and AA functions.
fix Issue 12738 - core.sys.posix.signal sigaction_t handler type mismatch
Merge pull request #849 from WalterBright/fix12738

[REG] fix Issue 12738 - core.sys.posix.signal sigaction_t handler type mismatch