c32_apply_mapping: New module. * lib/uchar.in.h (c32_apply_mapping): New declaration. * lib/c32_apply_mapping.c: New file. * m4/uchar_h.m4 (gl_UCHAR_H_REQUIRE_DEFAULTS): Initialize GNULIB_C32_APPLY_MAPPING. * modules/uchar (Makefile.am): Substitute GNULIB_C32_APPLY_MAPPING. * modules/c32_apply_mapping: New file.