FindwxWidgets: Fix parsing of cxxflags when include paths contain -D or -I
This fixes issue #16986 (closed): FindwxWidgets.cmake fails when the path to the package contains a -D or -I in the name.
This may also fix issues when the include paths contain spaces, but I have not tested that case.
Topic-rename: FindwxWidgets-fix-flag-parse
Edited by Brad King