realpath: Fixing undefined behaviour in the second test. If the call fails the resolved_name argument cannot be used for error checking because its state is undefined by SUSv2.
pipe: Changing the order of close and write error handling code. Errors in close could overwrite errno after write errors, returning incorrect error messages.
gmtime: Removed duplicate checks
Other fixes for fseek, rename, mktime, putwchar
This will allow us to redefine the exit function.
For example:
```
#define exit(code) { \
fprintf(stderr, "%s:%d: exit(%s) in function ‘%s’\n",
__FILE__, __LINE__, #code, __func__); \
_exit(code); \
}
```
Tibor Nagy