ncurses: install *.pc files (for pkg-config)

To make e.g. "pkg-config --cflags ncursesw" work.

The ncurses expression, when built in unicode/wide char mode, provides
backward compatibility symlinks from lib<name>.so to lib<name>w.so.
Provide similar symlinks for the *.pc files: <name>.pc -> <name>w.pc.