FTBFS: plugin_main.c:1:21: fatal error: gtk/gtk.h: No such file or directory

[peter green]

>/bin/bash ../libtool --tag=CC   --mode=compile gcc -DHAVE_CONFIG_H -I. -I..    -Wall -ggdb   -g -O2 -DSKINDIR=\"/usr/share/audacious\" -g -O2 -c -o plugin_main.lo plugin_main.c
>libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I.. -Wall -ggdb -g -O2 -DSKINDIR=\"/usr/share/audacious\" -g -O2 -c plugin_main.c  -fPIC -DPIC -o .libs/plugin_main.o
>plugin_main.c:1:21: fatal error: gtk/gtk.h: No such file or directory
It would appear the problem is that  "pkg-config --cflags audacious" no longer returns anything.

This leaves a few questions for the audacious maintainers (in cc, I've also cc'd the person who made the two 
most recent audacious uploads )

1: is it intentional that "pkg-config --cflags audacious" no longer returns anything?
2: if so do plugins have to be built against the same version of gtk that audacious is built against?
3: if so how should plugins like this find out what version of gtk audacious is built against?
4: if the answer to 2 is yes then should there be some system for generating binary 
   dependencies against a version of audacious built against the correct gtk?

Note: i'm just doing rc bug investigation, I have no relationship to this package.