config.status has been broken by issue 5780 "Accept GUILE 2 without extra configure options"

[David Kastrup]

If I previously did

GUILE_CONFIG=/usr/local/tmp/guile-1.8/bin/guile-config ./configure
./config.status --recheck

then the Guile configuration was reused.  If I now do

PKG_CONFIG_PATH=/usr/local/tmp/guile-1.8/lib/pkgconfig ./configure
./config.status --recheck

the configuration information is lost and configure reverts to the
system configuration.

In addition, PKG_CONFIG_PATH is not documented in our configuration or
with ./configure --help.

How to fix?

A documented option --with-guile-prefix or --with-libguile-prefix that
puts up a working configuration might be a reasonably transparent and
future-safe option.

Also now I don't think it made sense to _remove_ the GUILE_CONFIG
variable: if it's set, it seems worth heeding.  If it's unset, going via
pkgconfig may be the right way.  --with-libguile-prefix could pick the
right option underneath, checking that it is viable, and prefer using
PKG_CONFIG_PATH .

-- 
David Kastrup