build-sys: autodetect and use pkg-config for libselinux

build-sys: autodetect and use pkg-config for libselinux

Hi!
libselinux has a pkg-config file:

$ rpm -qf /usr/lib64/pkgconfig/libselinux.pc
libselinux-devel-2.0.98-alt1

$ cat /usr/lib64/pkgconfig/libselinux.pc
prefix=/usr
exec_prefix=${prefix}
libdir=${exec_prefix}/lib64
includedir=/usr/include

Name: libselinux
Description: SELinux utility library
Version: 2.0.98
URL: http://userspace.selinuxproject.org/
Libs.private: -lsepol
Libs: -lselinux
Cflags:

Patch for use pkg-config in attach.

--
Alexey Shabalin