All the separate pkg-config calls were done after reading:
http://tirania.org/blog/archive/2012/Oct-20.html
("Drowning Good Ideas with Bloat. The tale of pkg.m4."
by Miguel de Icaza)

But all the GNOME modules I contribute to use PKG_CHECK_MODULES or
AX_PKG_CHECK_MODULES for a library. With those macros, it shows all the
errors at once (if several libs are missing or too old) instead of
aborting at the first error.