devel/readline and pc file

[Greg Troxel <gdt%lexort.com@localhost>]

Readline has odd build/install targets, not explained:

BUILD_TARGET=           everything-libtool
INSTALL_TARGET=         install-libtool

and this leads to not installing the pkgconfig file, that upstream added
years ago, and which at least one other program expects.

Does anyone understand why readline doesn't install readline.pc?

Absent an explanation (in a comment committed to the Makefile!), I'll
presume this is just a bug.