canonicalize, canonicalize-lgpl: update module dependencies

canonicalize, canonicalize-lgpl: update module dependencies

The m4 files were checking whether canonicalize_file_name was
declared, but without enabling extensions, this would never
succeed.  Also, mingw failed to compile the module combination of
canonicalize-lgpl and sys_stat, due to a link error on lstat.

* modules/canonicalize (Depends-on): Add extensions, lstat,
pathmax, stdlib.
(Files): Drop pathmax.h.
(configure.ac): Adjust macro name.
* modules/canonicalize-lgpl (Depends-on): Add errno, extensions,
lstat, stdlib, sys_stat.
* m4/canonicalize.m4 (AC_FUNC_CANONICALIZE_FILE_NAME): Rename...
(gl_FUNC_CANONICALIZE_FILENAME_MODE): ...to this, and require
extensions.
* m4/canonicalize-lgpl.m4 (gl_CANONICALIZE_LGPL)
(gl_CANONICALIZE_LGPL_SEPARATE): Require extensions.
(gl_PREREQ_CANONICALIZE_LGPL): Assume unistd.h.
* lib/canonicalize.h (canonicalize_file_name): Use <stdlib.h>
declaration, if available.
* lib/canonicalize-lgpl.c [HAVE_READLINK]: Delete this condition;
we can rely on the readlink module.
(MAXSYMLINKS): Also consult SYMLOOP_MAX.
(includes): Use <unistd.h> unconditionally.

Signed-off-by: Eric Blake <ebb9@byu.net>