* lib/uchar.in.h (_GL_LARGE_CHAR32_T): New macro.
(c32tob): New declaration.
* lib/c32tob.c: New file.
* m4/uchar.m4 (gl_UCHAR_MODULE_INDICATOR, gl_UCHAR_H_DEFAULTS): New
macros.
(gl_UCHAR_H): Require gl_UCHAR_H_DEFAULTS.
* modules/uchar (Depends-on): Add snippet/c++defs.
(Makefile.am): Include c++defs.h and substitute GNULIB_C32TOB in
uchar.h.
* modules/c32tob: New file.
* tests/test-uchar.c: Verify that _GL_LARGE_CHAR32_T is correctly
defined.
* tests/test-uchar-c++.cc: Include signature.h. Test the signature of
c32tob.
* modules/uchar-c++-tests (Files): Add tests/signature.h.
* doc/posix-functions/wctob.texi: Mention the new module.