vim: move long_u from vim.h to types.h

Seems to make no difference to the main binary, but it helps the tests a bit
further along.

src/nvim/types.h

@@ -10,6 +10,11 @@
 
 #include <stdint.h>
 
+// Make sure long_u is big enough to hold a pointer.
+// On Win64, longs are 32 bits and pointers are 64 bits.
+// For printf() and scanf(), we need to take care of long_u specifically.
+typedef unsigned long long_u;
+
 /*
  * Shorthand for unsigned variables. Many systems, but not all, have u_char
  * already defined, so we use char_u to avoid trouble.