Recent testing has uncovered some hard-to-find bugs in printf's long
double support. This patch adds an extra long double path to the fuzzer
with minimal extra effort. While a more thorough long double fuzzer
would be useful, it would need to handle the non-standard cases of 80
bit long doubles such as unnormal and pseudo-denormal numbers. For that
reason, a standalone long double fuzzer is left for future development.
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