style: avoid strncpy

syntax-check seems to dislike strncpy.  The GNU Coreutils replaced
their uses of strncpy with stpncpy.

strlcpy is not an option.
  http://sources.redhat.com/ml/libc-alpha/2002-01/msg00159.html
  http://sources.redhat.com/ml/libc-alpha/2002-01/msg00011.html
  http://lists.gnu.org/archive/html/bug-gnulib/2004-09/msg00181.html

* src/glyphs.c: Use stpncpy.

lib/.gitignore

@@ -313,6 +313,7 @@
 /stdlib.h
 /stdlib.in.h
 /stpcpy.c
+/stpncpy.c
 /strchrnul.c
 /strchrnul.valgrind
 /strdup.c