Log Message:
pkgconf: update to 1.8.0.

Changes from 1.7.4 to 1.8.0:
----------------------------

* This is the last planned maintenance branch.  I see pkgconf as basically
  a finished tool at this point, and very few people were ultimately interested
  in libpkgconf.  So, from here on out, it will just be bug fixes only and
  very minor enhancements.

* Bug fixes:
  - Improved path handling on Windows to conform to what the MSYS2
    and Cygwin teams were already modifying pkgconf to do.
    Patches by Christoph Reiter.
  - Fix a minor memory leak relating to cross-personalities.
    Patch by Stone Tickle.
  - Fix static builds for Windows on Meson.
    Patch by Alexander Neumann.
  - Fix some edge cases with --redefine-prefix.
    Patch by midipix.
  - Do not prepend sysroot_dir if the .pc file does not exist in the
    sysroot.
    Patch by Sandro Mani.
  - Do not perform path filtering on default system include and library
    path lists.  This fixes consistency with other mechanisms that modify
    these path lists.

* Enhancements:
  - Document the --validate option in the manpage.
    Patch by orbea.