Inconsistency in file manipulation flag values between newlib (cross-compilation) and glibc (native)

[btsouts]

Describe the bug
Common file manipulation flags such as O_CREAT have different values in newlib and
native libc implementation (definitely in Linux). There operations such as creation of
a file fail. Related also to issue 164.

Example:

newlib-2.5.0.20170922/newlib/libc/include/sys/_default_fcntl.h:

#define _FOPEN (-1) /* from sys/file.h, kernel use only /
#define _FREAD 0x0001 / read enabled /
#define _FWRITE 0x0002 / write enabled /
#define _FAPPEND 0x0008 / append (writes guaranteed at the end) /
#define _FMARK 0x0010 / internal; mark during gc() /
#define _FDEFER 0x0020 / internal; defer for next gc pass /
#define _FASYNC 0x0040 / signal pgrp when data ready /
#define _FSHLOCK 0x0080 / BSD flock() shared lock present /
#define _FEXLOCK 0x0100 / BSD flock() exclusive lock present /
#define _FCREAT 0x0200 / open with file create /
#define _FTRUNC 0x0400 / open with truncation */

For Ubuntu GLIBC 2.27-3ubuntu1, in /usr/include/bits/fcntl-linux.h:

#define O_ACCMODE 0003
#define O_RDONLY 00
#define O_WRONLY 01
#define O_RDWR 02
#ifndef O_CREAT
#define O_CREAT 0100 /* Not fcntl. /
#endif
#ifndef O_EXCL
#define O_EXCL 0200 / Not fcntl. /
#endif
#ifndef O_NOCTTY
#define O_NOCTTY 0400 / Not fcntl. /
#endif
#ifndef O_TRUNC
#define O_TRUNC 01000 / Not fcntl. */

To Reproduce
Steps to reproduce the behavior:

1. Create an program that creates a new file for writing with fopen, i.e. fopen(filename, "w")
2. Compile for sunflower RISC-V and execute.
3. The target file should not exist.

Host OS (please complete the following information):

• OS: Ubuntu 18.04.4 LTS
• Kernel: 5.3.0-42-generic Cleanup for elf move #34~18.04.1-Ubuntu
• Libc version: Ubuntu GLIBC 2.27-3ubuntu1
• CC: gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0