title: Link errors with -ffast-math (-ffinite-math-only) and glibc 2.31
body: <p>Recently, glibc (namely with glibc 2.31, included in Ubuntu 20.04) seems to have removed families of functions like <code>__exp_finite()</code>.</p>
  <p>These functions were used when compiling with gcc's option <code>-ffinite-math-only</code> (or <code>-ffast-math</code>, which enables the said option).</p>
  <p>My problem is that I have <em>compiled closed sources</em> static libraries provided by third parties which have been presumably compiled with this flag and those libraries generate linking errors to missing math functions like <code>__exp_finite()</code>.</p>
  <p>My question is what is my better solution?</p>
  <ol>
  <li>Submit the issue to the third parties, ask them to remove the offending flag from their command line and wait (months...) ?</li>
  <li>Submit the issue to the glibc developpers, explaining that they broke compatibility with this build option ?</li>
  <li>Define myself the missing functions ?</li>
  <li>?</li>
  </ol>
  <p>I would prefer to omit solutions which involes compiling in a different environment than the native one provided by Ubuntu (and later probably other distribution as they upgrade glibc).</p>
  <p>Hopefully I have understood the problem correctly and any help is appreciated.</p>