Remove libdir from xcb-proto.pc
Added by 17ab095a ("add libdir/exec_prefix to xcb-xproto.pc") with the rationale of using it to find the python path, but later commits bd7a481a ("pkg-config: Add sysroot prefix") and be9c255b ("Adjust to automake 1.16.4 changes") make this directly accessible.
By removing libdir from the pkgconfig file, the file becomes identical for different ABIs.
Install xcb-proto to $(datarootdir)
... i.e. to /usr/share/pkgconfig.
Call AC_OUTPUT without arguments
configure.ac:22: warning: AC_OUTPUT should be used without arguments. configure.ac:22: You should run autoupdate.