"Since the 2.16 release of the glibc, 'gets' is not any more defined in the gnulib.
No m4 version synchronized with gnulib since  has been released yet."
This causes gets compile errors on systems with glibc >= 2.16 with sources that still assume the previous definition.
The following link contains a patch for the M4 source, that is supposed to fix this:
Above as the long version of 'Must brush up Google Fu',
See "man patch" for details on applying patches to source code