As of July 2018, this statement is no longer necessary.

makefiles. This does not work on some versions of make; bug introduced in
libpng version 1.6.11.

header with a custom header, via the make PNGLIBCONF_H_PREBUILT
macro.

of 'cp' where applicable, and applied other minor makefile changes.

problems with build scripts that search for config.h and find an
inappropriate one in the standard paths.

from the source files, along with "#define PNG_EXPOSE_INTERNAL_STRUCTURES"
and "#define PNG_NO_PEDANTIC_WARNINGS" (John Bowler).
Also created new pngdebug.h and moved debug definitions there.

and added "#define PNG_NO_PEDANTIC_WARNINGS" in the libpng source files.