[tlbuild] VERBOSE=1 -> show build-log.txt

[Karl Berry]

A contributor on the automake mailing list reported that
  make check VERBOSE=1
cats test-suite.log to stdout if failure, as we have wanted (especially)
for the autobuilds on inaccessible systems.
http://lists.gnu.org/archive/html/automake/2018-09/msg00015.html

As far as I can tell from the sources, that is all that VERBOSE=1 does
(not the best choice of variable name).

So I've changed the TL ./Build script to automatically do that (r48808).
If for some reason you don't want it, you can set the envvar
TL_MAKE_VERBOSE to the empty string (or a space, or whatever) before
calling that.

If you don't use the Build script, you may want to add this to your
build procedures. Happy compiling! -k

P.S. Most of the dvipdfm-x tests failed for me, so I got to experience
the new behavior first hand. I'll look at that tomorrow if need be,
though most likely Akira will get there first.