Move the malloc helpers out of misc.c.

Now they live in their own file memory.c. The advantage of this is
that you can link them into a binary without also pulling in the rest
of misc.c with its various dependencies on other parts of the code,
such as conf.c.

windows/winstuff.h

@@ -693,4 +693,15 @@ char *get_jumplist_registry_entries(void);
 #define CLIPUI_DEFAULT_MOUSE CLIPUI_EXPLICIT
 #define CLIPUI_DEFAULT_INS CLIPUI_EXPLICIT
 
+#ifdef MINEFIELD
+/*
+ * Definitions for Minefield, PuTTY's own Windows-specific malloc
+ * debugger in the style of Electric Fence. Implemented in winmisc.c,
+ * and referred to by the main malloc wrappers in memory.c.
+ */
+void *minefield_c_malloc(size_t size);
+void minefield_c_free(void *p);
+void *minefield_c_realloc(void *p, size_t size);
+#endif
+
 #endif