devel/libunistring: Update 1.4.1 => 1.4.2

Changelog:

• Prepare for 1.4.2 release.
  • version.sh: Bump version number, date, gnulib version.
  • README: Update version.
  • NEWS: Update.
• Sync with gnulib.
  • lib/unistring/cdefs.h: Update from gnulib/m4/gnulib-common.m4.
• (_GL_UNNAMED): New macro.
• (_UC_UNNAMED): Apply "New C macro _GL_UNNAMED".
• Make the generated <unistring/stdint.h> more usable in C++ mode.
  • lib/Makefile.am (unistring/stdint.h): In C++ 11 or newer mode, just use <cstdint>.

PR: 293435