fixed MXE once and for all

thanks to @fgsfdsfgs, this is the final thing needed for MXE support

include/PR/os_libc.h

@@ -3,14 +3,28 @@
 
 #include "ultratypes.h"
 
-// Old deprecated functions from strings.h, replaced by memcpy/memset.
-#ifdef NO_BZERO
+// old bstring functions that aren't present on some platforms
+
+#if defined(__APPLE__)
+
+// macOS libc has them
+#include <strings.h>
+
+#elif defined(_POSIX_C_SOURCE) && (_POSIX_C_SOURCE >= 200809L)
+
+// there's no way that shit's defined, use memcpy/memset
 #include <string.h>
-#define bzero(buf, size) memset((buf), 0, (size))
-#define bcopy(src, dst, size) memcpy((dst), (src), (size))
+#undef bzero
+#undef bcopy
+#define bzero(buf, len) memset((buf), 0, (len))
+#define bcopy(src, dst, len) memcpy((dst), (src), (len))
+
 #else
+
+// hope for the best
 extern void bcopy(const void *, void *, size_t);
 extern void bzero(void *, size_t);
+
 #endif
 
 #endif /* !_OS_LIBC_H_ */