Fix -Werror failure on Alpine/MUSL libc & GCC 10
#27
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`poll.h` is the POSIX standard include location, and MUSL libc issues a warning (which infnoise's `-Werror` in CFLAGS makes into an error). For more context: - [Linux manpage for `poll(2)`][1] - [Open Group UNIX Specification][2] - [Relevant discussion over at the `emscripten` project][3] [1]: https://man7.org/linux/man-pages/man2/poll.2.html [2]: https://pubs.opengroup.org/onlinepubs/7908799/xsh/poll.h.html [3]: emscripten-core/emscripten#5447 (comment)
The return type of `getc(3)` is a signed integer, with negative values indicating an error. The changed line stored the return value in an *unsigned* integer, then tested it against a negative error constant, so the error condition would never be detected. This also results in a warning on GCC 10. Further information: - [`getc(3)`](https://man7.org/linux/man-pages/man3/fgetc.3.html) - [C FAQ question 12.1](http://c-faq.com/stdio/getcharc.html)
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Two compiler warnings result in a build failure. One is standards pedantry from MUSL libc, the other is a mishandled error value that GCC 10 issues a warning for. See details in PR commit messages.