Update linking on Windows for upcoming version of Rtools.

[kalibera]

This updates the package to link on Windows against an upcoming version of Rtools, where the used libraries need more dependencies. It also uses pkg-config, when available, which should reduce the frequency of updates needed to match updates in Rtools.

[nx10]

Thank you very much @kalibera !

[HenningLorenzen-ext-bayer]

Also takes care of a linking error when building with R 4.2 👍

   g++ -Wl,-S -shared -s -static-libgcc -o unigd.dll tmp.def base_64.o compress.o cpp11.o draw_data.o page_store.o plot_history.o r_thread_posix.o r_thread_win32.o renderer_cairo.o renderer_json.o renderer_meta.o renderer_strings.o renderer_svg.o renderer_tikz.o renderers.o unigd.o unigd_dev.o unigd_external.o uuid.o -lcairo -lpixman-1 -lfontconfig -lncrypt -lksecdd -lbcrypt -lexpat -lharfbuzz_too -lfreetype_too -lharfbuzz -lfreetype -lpng16 -lpng -lbz2 -lgdi32 -lintl -liconv -lz -lcfitsio -ltiff -ltiffxx -ljpeg -lzstd -lwebp -lsharpyuv -llzma -LC:/rtools42/x86_64-w64-mingw32.static.posix/lib/x64 -LC:/rtools42/x86_64-w64-mingw32.static.posix/lib -LC:/Users/[redacted]/R/R-4.2.3patched/bin/x64 -lR
   C:\rtools42\x86_64-w64-mingw32.static.posix\bin/ld.exe: cannot find -lsharpyuv