[libgfortran,committed] Cleanups

[FX]

Committed the two attached patches doing some minor cleanup in libgfortran:

  - removed unused “min” macro in io/unix.c
  - remove some unused configure checks (functions we check for but don’t use 
the result)

Regtested on x86_64-apple-darwin15, then committed separately.

FX

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z2.diff
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