Fix build if taglib is not available

If the taglib-config executable is not available, cmake/FindTaglib.cmake
searches directly for the libraries using find_library_with_debug().
This function is only available with KDELibs4Support;  however, on all
platforms apart from Win32 it is equivalent to find_library().  Just use
the latter directly.

CCMAIL:	jr@jriddell.org, elvis.angelaccio@kde.org