Add automatic generation of headers

- The 'stripdecls.py' script replaces declarations in all headers by includes to
  generated headers.
  `ag '#\s*if(?!ndef NEOVIM_).*((?!#\s*endif).*\n)*#ifdef INCLUDE_GENERATED'`
  was used for this.
- Add and integrate gendeclarations.lua into the build system to generate the
  required includes.
- Add -Wno-unused-function
- Made a bunch of old-style definitions ANSI

This adds a requirement: all type and structure definitions must be present
before INCLUDE_GENERATED_DECLARATIONS-protected include.

Warning: mch_expandpath (path.h.generated.h) was moved manually. So far it is
the only exception.

src/nvim/memory.h

@@ -1,43 +1,10 @@
 #ifndef NVIM_MEMORY_H
 #define NVIM_MEMORY_H
 
-#include "nvim/func_attr.h"
-#include "nvim/types.h"
+#include <stddef.h>
 #include "nvim/vim.h"
 
-void *try_malloc(size_t size) FUNC_ATTR_MALLOC FUNC_ATTR_ALLOC_SIZE(1);
-
-void *verbose_try_malloc(size_t size) FUNC_ATTR_MALLOC FUNC_ATTR_ALLOC_SIZE(1);
-
-void *xmalloc(size_t size)
-  FUNC_ATTR_MALLOC FUNC_ATTR_ALLOC_SIZE(1) FUNC_ATTR_NONNULL_RET;
-
-void *xcalloc(size_t count, size_t size)
-  FUNC_ATTR_MALLOC FUNC_ATTR_ALLOC_SIZE_PROD(1, 2) FUNC_ATTR_NONNULL_RET;
-
-void *xrealloc(void *ptr, size_t size)
-  FUNC_ATTR_WARN_UNUSED_RESULT FUNC_ATTR_ALLOC_SIZE(2) FUNC_ATTR_NONNULL_RET;
-
-void *xmallocz(size_t size) FUNC_ATTR_MALLOC FUNC_ATTR_NONNULL_RET;
-
-void *xmemdupz(const void *data, size_t len) FUNC_ATTR_NONNULL_RET;
-
-char * xstrdup(const char *str)
- FUNC_ATTR_MALLOC FUNC_ATTR_WARN_UNUSED_RESULT FUNC_ATTR_NONNULL_RET;
-
-char * xstrndup(const char *str, size_t len)
- FUNC_ATTR_MALLOC FUNC_ATTR_WARN_UNUSED_RESULT FUNC_ATTR_NONNULL_RET;
-
-char *xstpcpy(char *restrict dst, const char *restrict src);
-
-char *xstpncpy(char *restrict dst, const char *restrict src, size_t maxlen);
-
-size_t xstrlcpy(char *restrict dst, const char *restrict src, size_t size);
-
-void *xmemdup(const void *data, size_t len)
- FUNC_ATTR_MALLOC FUNC_ATTR_WARN_UNUSED_RESULT FUNC_ATTR_NONNULL_RET;
-
-void do_outofmem_msg(size_t size);
-void free_all_mem(void);
-
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "memory.h.generated.h"
 #endif
+#endif  // NVIM_MEMORY_H