stdlib, string, wchar: Improve GCC 11 allocation-deallocation checking. * 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.