doc: Fix target_{word_size,pointer_width} renaming

Update the reference page to the change in #20680.

Author: lukasoyen

src/doc/reference.md

@@ -2162,7 +2162,7 @@ fn needs_foo_or_bar() {
 
 // This function is only included when compiling for a unixish OS with a 32-bit
 // architecture
-#[cfg(all(unix, target_word_size = "32"))]
+#[cfg(all(unix, target_pointer_width = "32"))]
 fn on_32bit_unix() {
   // ...
 }
@@ -2190,9 +2190,9 @@ The following configurations must be defined by the implementation:
 * `target_os = "..."`. Operating system of the target, examples include
   `"win32"`, `"macos"`, `"linux"`, `"android"`, `"freebsd"`, `"dragonfly"`,
   `"bitrig"` or `"openbsd"`.
-* `target_word_size = "..."`. Target word size in bits. This is set to `"32"`
-  for targets with 32-bit pointers, and likewise set to `"64"` for 64-bit
-  pointers.
+* `target_pointer_width = "..."`. Target pointer width in bits. This is set
+  to `"32"` for targets with 32-bit pointers, and likewise set to `"64"` for
+  64-bit pointers.
 * `unix`. See `target_family`.
 * `windows`. See `target_family`.