* Add ctl utility.h
Implements forward, move, swap, and declval. This commit also adds a def
for nullptr_t to cxx.inc. We need it now because the CTL headers stopped
including anything from libc++, so we no longer get their basic types.
* Use ctl::swap in string
The STL spec says that swap is located in the string_view header anyawy.
Performance-wise this is a noop, but it’s slightly cleaner.
This replaces the STL <new> header. Mainly, it defines a global operator
new and operator delete, as well as the placement versions of these. The
placement versions are required to not get compile errors when trying to
write a placement new statement.
Each of these operators is defined with many, many different variants. A
glance at new.cc is recommended followed by a chaser of the Alexandrescu
talk "std::allocator is to Allocation as std::vector is to Vexation". We
must provide a global-namespace source-level definition of each operator
and it is illegal for any of them to be marked inline, so here we are.
The upshot is that we no longer need to include <new>, and our optional/
vector headers are self-contained.
Manually manage the lifetime of `value_` by using an anonymous
`union`. This fixes a bunch of double-frees and double-constructs.
Additionally move the `present_` flag last. When `T` has padding
`present_` will be placed there saving `alignof(T)` bytes from
`sizeof(optional<T>)`.
