[do-not-upstream][semihost] open sys call doesn't handle "rb+" mode

According to the ISO/IEC_9899_1999, section:7.19.5.3 Opening file with `r+` mode just open text file for update (reading and writing) but dosen't create it. if the file isn't exist `open()` returns NULL.

So, to create and open a file to update (reading and writing), we should open with "a+" or "w+" modes.

Signed-off-by: Mostafa Salman <mostafas@synopsys.com>

Author: mostafa-salmaan

semihost/open.c

@@ -69,8 +69,10 @@ open(const char *pathname, int flags, ...)
 	default:
 		if (flags & O_TRUNC)
 			semiflags = SH_OPEN_W_PLUS_B;	/* 'wb+' */
-		else
+		else if (flags & O_APPEND)
 			semiflags = SH_OPEN_A_PLUS_B;	/* 'ab+' */
+		else
+			semiflags = SH_OPEN_R_PLUS_B;	/* 'rb+' */
 		break;
 	}