Merge pull request #1973 from YosysHQ/eddie/fix1966

tests: fix various/plugin.sh when PREFIX != /usr/local/share

tests/various/plugin.sh

@@ -1,6 +1,8 @@
 set -e
 rm -f plugin.so
 CXXFLAGS=$(../../yosys-config --cxxflags)
-CXXFLAGS=${CXXFLAGS// -I\/usr\/local\/share\/yosys\/include/ -I..\/..\/share\/include}
+DATDIR=$(../../yosys-config --datdir)
+DATDIR=${DATDIR//\//\\\/}
+CXXFLAGS=${CXXFLAGS//$DATDIR/..\/..\/share}
 ../../yosys-config --exec --cxx ${CXXFLAGS} --ldflags -shared -o plugin.so plugin.cc
 ../../yosys -m ./plugin.so -p "test" | grep -q "Plugin test passed!"