Version 3.15 introduces the <PREFIX>_KEYWORDS_MISSING_VALUES of the
cmake_parse_arguments() function, which is used in generate_g1a() and
generate_g3a(), so there is no way to bring it further down for free.
The FindPNG module fails catastrophically on Mac OS because it searches
for the library and header independently, and ends up pulling a
completely unrelated header from a random framework.
Lephenixnoir