Sema now properly handles alloc_inferred and alloc_inferred_mut ZIR
instructions inside a comptime execution context. In this case it
creates Decl objects and points to them with the new `decl_ref_mut`
Value Tag. `storePtr` is updated to mutate such Decl types and values.
In this case it destroys the old arena and makes a new one, preventing
memory growth during comptime code execution.
Additionally:
* Fix `storePtr` to emit a compile error for a pointer comptime-known
to be undefined.
* Fix `storePtr` to emit runtime instructions for all the cases that a
pointer is comptime-known but does not support comptime
dereferencing, such as `@intToPtr` on a hard-coded address, or an
extern function.
* Fix `ret_coerce` not coercing inside inline function call context.
Conflicts:
* doc/langref.html.in
* lib/std/enums.zig
* lib/std/fmt.zig
* lib/std/hash/auto_hash.zig
* lib/std/math.zig
* lib/std/mem.zig
* lib/std/meta.zig
* test/behavior/alignof.zig
* test/behavior/bitcast.zig
* test/behavior/bugs/1421.zig
* test/behavior/cast.zig
* test/behavior/ptrcast.zig
* test/behavior/type_info.zig
* test/behavior/vector.zig
Master branch added `try` to a bunch of testing function calls, and some
lines also had changed how to refer to the native architecture and other
`@import("builtin")` stuff.
