result when integers appear on both sides of a compare.  Worked around the
  others by forcing the strict-overflow setting in the relevant functions to
  a level where they are not reported.
Changed "FALL THROUGH" comments to "FALLTHROUGH" because GCC doesn't like
  the space.
Worked around some C-style casts from (void*) because g++ 5.4.0 objects
  to them.
Increased the buffer size for 'sprint' to pass the gcc 7.1.0 'sprint
  overflow' check that is on by default with -Wall -Wextra.

enabled.

possible integer overflow (Bug report by John Bowler).

or disable all hardware optimizations with one flag.
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Glenn R-P

PNG_ARM_NEON_IMPLEMENTATION == 2 to exclude some definitions that assembler
cannot recognize.

("typedef" directive is unrecognized by the assembler).

compression buffer (bug report by Brian Baird).  This bug was introduced in
libpng-1.6.0.

to update zlib.net URLs