\addlyrics causes failure and spurious "no music in score" warning

[Connor Harris]

I usually work with Frescobaldi's templates for LilyPond choral music.  I
recently upgraded from 2.15.30 to 2.15.38 (both built from source on an Arch
Linux machine) and all of my choral-music files stopped compiling.  A typical
compilation log (for my minimal example below):

Starting lilypond 2.15.38 [test-composition.ly]...
Processing `/home/connor/test-composition.ly'
Parsing...
warning: no music found in score
Success: compilation successfully completed
Completed successfully in 1.2".

The program "succeeds" (returns exit status 0), but produces no .pdf file as
output.  The \addlyrics command seems to be causing the problem: the closest
thing to a minimal example I could find is this:

\version "2.15.38"

soprano = c'1

sopranoVerse = \lyricmode {}

\score {
   \new Staff \soprano \addlyrics { \sopranoVerse }
}

This produces the above log; commenting out "\addlyrics { \sopranoVerse }"
creates a file that compiles correctly.

Strangely, rebuilding and installing 2.15.30, which I had previously used
without incident, caused the same errors to occur; as did rebuilding 2.15.25. 
Arch Linux's package of Lilypond (2.14.2) works fine, though, which raises the
possibility of a bug in a new version of gcc or similar. That seems quite
unlikely, but I may try building Lilypond with an older version of gcc and
running the same tests.

- Connor Harris