Ubuntu/Debian style file placement are ;
No.1 libudev.so and libudev.so.1 in /lib or /lib/arch/
No.2 libudev.h in /usr/include
No.3 libudev.pc in /usr/lib/pkgconfig or /usr/lib/arch/pkgconfig
Current Makefile can install No.1 and No.2 pattern by
"make PREFIX=/usr LIBDIR=/lib INCLUDEDIR=/usr/include install",
but it can't install No.3 pattern.
This patch added PKGCONFIGDIR environment variable to achieve all install pattern by
"make PREFIX=/usr LIBDIR=/lib INCLUDEDIR=/usr/include PKGCONFIGDIR=/usr/lib install"