harmonic dots breaks GUB?

[Graham Percival]

The release-2.14 branch isn't compiling the docs; it appears to die on
this file:

  <e a\harmonic>2.  <c g'\harmonic>4
  \set harmonicDots = ##t
  <e a\harmonic>2.  <c g'\harmonic>4

by "appears to die", I mean that the main make reports an error, but
the job-specific logfiles just ends like this:

...
[/main/src/gub/target/linux-x86/root/usr/share/lilypond/current/fonts/otf/emmentaler-18.otf]
[/main/src/gub/target/linux-x86/root/usr/share/lilypond/current/fonts/otf/emmentaler-23.otf]
[century_schoolbook_l_serif_3.0673828125


That's literally it.  No segfault, no "ghostscript cannot find this
font", no "guile has encountered an error" -- the log file just seems
to end in the middle of a compile.  It doesn't even finish writing the
final ]  that should be at the end of the [century_schooolbook...
line.

This is not the first file it tries to compile.  It's not even the
first file that this particular forked process is trying to compile.
I'm completely baffled.  I've tried it twice from my normal release
state (no *lilypond* inside target/ but everything else compiled), and
one from complete scratch (rm -rf target/ ).


NB: this is not the first weird GUB-build error; I remember having
something weird in the 2.13.47 build, but since it was two weeks since
the previous release, there was lots of work on patches, and I didn't
want to hold stuff back, I just restarted the doc build and it managed
to finish.  Very naughty of me, I know.

I'm going to do the same thing right now -- get a 2.13.48 out there
with very naughty manual hacking.  It's not going to be a release
candidate, though.

Can anybody else build lilypond-doc with GUB?  Either with your own
personal GUB branch, or with the release-2.14 branch?  (could this be
as simple as needing to bump the ulimit number of files/buffers/etc ?
I can't remember if we normally get a sensible error message if we hit
those limits)

Cheers,
- Graham