sys/user.h provides definitions for registers. It would previously get
merged into the sys module which could result in it being multiply
included (as in the case of libdispatch). Add an explicit submodule.
Noticed when building libdispatch on Linux AArch64.
Remove 16 concrete init(stringInterpolationSegment:) overloads and
replace them with 3 generic overloads, significantly reducing the
exponential blow-up from larger string interpolations.
Fixes rdar://problem/29389887.
For this we are linking the new re-mangler instead of the old one into the swift runtime library.
Also we are linking the new de-mangling into the swift runtime library.
It also switches to the new mangling for class names of generic swift classes in the metadata.
Note that for non-generic class we still have to use the old mangling, because the ObjC runtime in the OS depends on it (it de-mangles the class names).
But names of generic classes are not handled by the ObjC runtime anyway, so there should be no problem to change the mangling for those.
The reason for this change is that it avoids linking the old re-mangler into the runtime library.
The old method of constructing a mangled class name does not work anymore with the new mangling scheme.
Also, by using the re-mangler, _typeByName now works with class names containing non-ascii characters.
This breaks the build on exherbo, which uses target tripled linker
names. Furthermore, the default name on unix-ish systems for the linker
is `ld`. This can be a symlink to a specific implementation, usually
named as ld.<name> (e.g. `ld.bfd` or `ld.gold`). Use the cmake variable
for the linker rather than hardcoding the name.
Data can encapsulate it’s own sub-sequence type by housing a range of the slice in the structural type for Data. By doing this it avoids the API explosion of supporting all APIs that take Data would need overloads to take a slice of Data. This does come at a small conceptual cost: any index based iteration should always account for the startIndex and endIndex of the Data (which was an implicit requirement previously by being a Collection). Moreover this prevents the requirement of O(n) copies of Data if it is never mutated while parsing sub sequences; so more than an API amelioration this also could offer a more effecient code-path for applications to use.
