* lib/stdlib.in.h (aligned_alloc): For GCC >= 11: Declare also when the
platform already declares the function or when the module
'aligned_alloc' is not in use.
(calloc): For GCC >= 11: Declare nearly always.
(canonicalize_file_name): For GCC >= 11: Declare also when the platform
already declares the function or when the module 'canonicalize-lgpl' is
not in use.
(malloc, realloc): For GCC >= 11: Declare nearly always.
* lib/malloc.in.h: Remove redundant include.
(memalign): For GCC >= 11: Declare also when the platform already
declares the function or when the module 'memalign' is not in use.
* lib/string.in.h: Include <stdlib.h> always.
(strdup): For GCC >= 11: Declare also when the platform already declares
the function or when the module 'strdup' or 'strdup-posix' is not in
use.
* lib/wchar.in.h: Include <stdlib.h> always.
(wcsdup): For GCC >= 11: Declare also when the platform already declares
the function or when the module 'wcsdup' is not in use.
* modules/free-posix (Depends-on): Add string, wchar.