Test fgets_eagain fails on FreeBSD-amd64

According to the BSD Buildbot

util/fgets_eagain: 
  FAIL src/test/test_util.c:3952: assert(retptr OP_EQ buf): 0x0 vs 0x7fffffffe944
  [fgets_eagain FAILED]

This means that fgets returns a null pointer on partial lines instead of the buffer as expected.

Previously this test was passing but started failing with build #105. Looking at the changes to libc it looks like this is caused by revision 305413 (which was added earlier in the same month the test started failing).

I'm unsure whether FreeBSD is right and other libc implementations are wrong or the other way around.

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