Use m4_pattern_ignore for some PKG_* macros
Use m4_pattern_ignore for some PKG_* macros

It makes more sense to use the provided m4_pattern_ignore()
macro than writing our own error messages.

Yes, our own error message could be more helpful to the
uninitiated user by mentioning the package and the m4 file
name to install which provide the required macro.

However, those file names and package names can and do change
with time or by operating system.

gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2