[geos] Install pc file also for Windows

[dg0yt]

• What does your PR fix?

  This PR adds pkg-config file installation for Windows.
  With port vcpkg-pkgconfig-get-modules and pkg-config parameter --msvc-syntax, the geos.pc file can be used to easily lookup the target link libraries needed for geos in particular in nmake builds. Cf. [libspatialite] Use pkgconfig for nmake and autotools #20480 (libspatite), [gdal:x64-windows-static] missing geos dependencies #15526 (gdal).
  This may facilitate removing the custom debug postfix in a future revision.
  (I'm going to make similar changes to other geographic packages.)

  This PR also fixes a build-time warning on stdout.

• Which triplets are supported/not supported? Have you updated the CI baseline?

  unchanged, no

• Does your PR follow the maintainer guide?

  yes

• If you have added/updated a port: Have you run ./vcpkg x-add-version --all and committed the result?

  yes

[BillyONeal]

Thanks for the bug fix and sorry about the macos PR hiccups!