POP3_TYPE_ANY, or ~0, is written to pop3c->preftype in lib/pop3c.c, an
unsigned int variable. The result of ~0 is -1, which caused a warning
due to writing a negative number to an unsigned variable. To fix this,
make the expression ~0U so that its value is considered the unsigned
number UINT_MAX which is what SASL_AUTH_ANY does in curl_sasl.h.
/* Authentication type values */
#define POP3_TYPE_NONE 0
-#define POP3_TYPE_ANY ~0
+#define POP3_TYPE_ANY ~0U
/* This is the 5-bytes End-Of-Body marker for POP3 */
#define POP3_EOB "\x0d\x0a\x2e\x0d\x0a"