Also failures on Gentoo: here b is positive (possibly +inf), and c is finite, so we expect an infinite result. Instead, we're apparently getting a NaN. I don't have a good guess about what's causing this: the rest of the tests are passing, so it's unlikely that we're using a bad FMA emulation. Maybe an optimization bug?

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ERROR: test_fma_infinities (test.test_math.FMATests)
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Traceback (most recent call last):
  File "/buildbot/buildarea/3.x.ware-gentoo-x86.installed/build/target/lib/python3.7/test/test_math.py", line 1482, in test_fma_infinities
    self.assertEqual(math.fma(math.inf, b, c), math.inf)
ValueError: invalid operation in fma