Bug#895002: libgtk2.0-dev: AM_PATH_GTK_2_0 misuses AC_PATH_PROG

[Helmut Grohne]

Package: libgtk2.0-dev
User: helmutg at debian.org
Usertags: rebootstrap
Control: affects -1 + src:gcx

This is essentially a clone of #894069. Same problem. Same patch. I know
AM_PATH_GTK_2_0 is deprecated, but gcx uses it and thus stumbles over
its use of AC_PATH_PROG finding the build architecture pkg-config.

I'm not sure what the EOL plan for gtk2 is, but if EOL is close, I'm
happy if you turn this into a bug asking gcx to move away from gtk2
instead. Seems like ubuntu started gtk2 removal two years ago:
https://bugs.launchpad.net/ubuntu-gnome/+bug/1585903

E.g. for qt, we do not try to support cross compilation with qt4,
because it is pending removal. I'm happy to exclude all of gtk2 if that
is pending removal as well.

Helmut