Define constants for _open and silence some warnings

src/windows/port.h

@@ -70,8 +70,11 @@
  * 4715: for some reason VC++ stopped realizing you can't return after abort()
  * 4800: we know we're casting ints/char*'s to bools, and we're ok with that
  * 4996: Yes, we're ok using "unsafe" functions like fopen() and strerror()
+ * 4312: Converting uint32_t to a pointer when testing %p
+ * 4267: also subtracting two size_t to int
+ * 4722: Destructor never returns due to abort()
  */
-#pragma warning(disable:4244 4251 4355 4715 4800 4996)
+#pragma warning(disable:4244 4251 4355 4715 4800 4996 4267 4312 4722)
 
 /* file I/O */
 #define PATH_MAX 1024
@@ -86,6 +89,11 @@
 #define pclose  _pclose
 #define R_OK    04           /* read-only (for access()) */
 #define S_ISDIR(m)  (((m) & _S_IFMT) == _S_IFDIR)
+
+#define O_WRONLY _O_WRONLY
+#define O_CREAT _O_CREAT
+#define O_EXCL _O_EXCL
+
 #ifndef __MINGW32__
 enum { STDIN_FILENO = 0, STDOUT_FILENO = 1, STDERR_FILENO = 2 };
 #endif