Mac OSX install libchromaprint.pc

For macports, we believe the libchromaprint.pc should be installed

"However, in MacPorts we are often using Linux-style builds hence the need for the pkg-config file when the non-framework library is being installed. So I think using NOT (APPLE AND BUILD_FRAMEWORK) or just NOT BUILD_FRAMEWORK would be more appropriate for MacPorts."

I'll patch our macports version - any opinion?