CTL: utility.h, use ctl::swap in string (#1227)

* 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.

ctl/vector.h

@@ -3,9 +3,7 @@
 #ifndef COSMOPOLITAN_CTL_OPTIONAL_H_
 #define COSMOPOLITAN_CTL_OPTIONAL_H_
 #include "new.h"
-#include <__utility/forward.h>
-#include <__utility/move.h>
-#include <__utility/swap.h>
+#include "utility.h"
 
 namespace ctl {
 
@@ -173,7 +171,7 @@ struct vector
             return;
         T* newP = new T[c2];
         for (size_t i = 0; i < n; ++i)
-            newP[i] = std::move(p[i]);
+            newP[i] = ctl::move(p[i]);
         delete[] p;
         p = newP;
         c = c2;
@@ -197,7 +195,7 @@ struct vector
             c2 += c2 >> 1;
             reserve(c2);
         }
-        new (&p[n]) T(std::forward<T>(e));
+        new (&p[n]) T(ctl::forward<T>(e));
         ++n;
     }
 
@@ -209,7 +207,7 @@ struct vector
             c2 += c2 >> 1;
             reserve(c2);
         }
-        new (&p[n]) T(std::forward<Args>(args)...);
+        new (&p[n]) T(ctl::forward<Args>(args)...);
         ++n;
     }
 
@@ -236,9 +234,9 @@ struct vector
 
     void swap(vector& other) noexcept
     {
-        std::swap(n, other.n);
-        std::swap(c, other.c);
-        std::swap(p, other.p);
+        ctl::swap(n, other.n);
+        ctl::swap(c, other.c);
+        ctl::swap(p, other.p);
     }
 };