#2568 With a separate build directory, the list of terminals is missing in the info manual

[Vincent Lefevre]

When gnuplot 5.4.5 and earlier is built with a separate build directory (as done in Debian), the info manual is not built correctly: the list of terminals is absent (so, a large part of the documentation is missing) and as a consequence, its structure is also incorrect, which breaks info navigation. See details in my Debian bug report:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=989029

The cause is that the docs/doc2texi.el file contains a path relative to the current directory to find the .trm files instead of being relative to the source directory:

(defvar d2t-terminal-directory (expand-file-name "../term/")
  "Location of .trm files in gnuplot source tree.")

The docs/Makefile.am file defined a variable T for that:

T = $(top_srcdir)/term/

Then, I don't know the best way to pass it to the docs/doc2texi.el code.

[Vincent Lefevre]

The broken navigation is actually caused by a different bug in doc2texi.el; see bug #2575 I've just reported.

This one, about the incorrect relative path, is just about the missing list of terminals, and the corresponding Debian bug is finally: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=989028