meson: libelf.pc is not always available
meson: libelf.pc is not always available

libelf, just like libc, is not a single project. It is an interface
which can be implemented independently by different operating systems.
Therefore, we cannot expect all systems to provide a .pc file, and we
should fallback to cc.find_library and cc.has_function like what we
already do in autotools build.

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib