When tm.texi.in is updated in the source tree, the following message
gets displayed:

Verify that you have permission to grant a GFDL license for all
new text in tm.texi, then copy it to <gcc src dir>/gcc/doc/tm.texi.

Having been myself and some colleagues confused several time by that
message as to what tm.texi to copy, I think it would be clearer to
indicate the absolute path for the source as well. This patch achieves
that.

2018-08-10  Thomas Preud'homme  <thomas.preudhomme@linaro.org>

    gcc/
    * Makefile.in: Clarify which tm.texi to copy over to assert the
    right to grant a GFDL license for all.

From-SVN: r263464