Rather than scanning through the generic parameters and generic requirements
each time we form a key for the generic metadata cache, compute these
values once, when the cache itself is first initialized.
Recent builds of clang give C++ globals of a type global constructors if they have a mix of explicitly initialized and default-initialized fields, apparently.
To minimize code size and VM live set, we try to funnel all one-time initialization through swift_once instead of mixing it with the C++ runtime's support for lazy static initialization.
- Added missing ifdef guard in PointerIntEnum header
- Consistent naming convention for ifdef guards
- Consistent 'end namespace swift'
- Consistent single EOL at end of header files
The C++ ABI for static locals is a bit heavy compared to dispatch_once; doing this saves more than 1KB in runtime code size. Dispatch_once/call_once is also more likely to be hot because it's also used by Swift and ObjC code.
Alas, llvm::get_execution_seed() from llvm/ADT/Hashing.h still inflicts one static local initialization on us we can't override (without forking Hashing.h, anyway).
