-lm -ldl -lpthread are _not_ needed in Libs (since the alsa interface
doesn't depend on libm, libdl or libpthread interface) and just bring
unneeded dependencies. These should rather be put in Libs.private:
Libs: -L${libdir} -lasound
Libs.private: -lm -ldl -lpthread
See ALSA bug#2212 .