ARM semihosting: win32 and cygwin fixes

Cygwin would fail to reopen a previously written file if the mode is
not given.

Simplified converting the open flags and made sure the win32 O_BINARY
bit is set.

Added define for systems that do not support O_BINARY.

Signed-off-by: Spencer Oliver <ntfreak@users.sourceforge.net>

src/helper/replacements.h

@@ -40,6 +40,12 @@
 #define ENOTSUP 134		/* Not supported */
 #endif
 
+/* for systems that do not support O_BINARY
+ * linux being one of them */
+#ifndef O_BINARY
+#define O_BINARY 0
+#endif
+
 #ifndef HAVE_SYS_TIME_H
 
 #ifndef _TIMEVAL_DEFINED