AIX: Revert timespec.tv_nsec to c_long and use st_timespec for stat

[xingxue-ibm]

Description

The previous commit #4750 changed the tv_nsec field of the timespec structure to i32 to match the output types of system calls fstat and fstat64. However, it turns out that other system calls, such as nanosleep, expect the tv_nsec field to be of type c_long. This patch restores the type of timespec.tv_nsec to c_long and uses struct st_timespec in struct stat and struct stat64 for the fstat and fstat64 system calls, aligning these definitions with those in the AIX <sys/stat.h> header.

In <sys/stat.h>:

/* internal timespec to preserve binary compatibility */
typedef struct st_timespec {
        time_t  tv_sec;         /* seconds */
        int     tv_nsec;        /* and nanoseconds */
} st_timespec_t;

Sources

Checklist

• Relevant tests in libc-test/semver have been updated
• No placeholder or unstable values like *LAST or *MAX are
  included (see #3131)
• Tested locally (cd libc-test && cargo test --target mytarget);
  especially relevant for platforms that may not be checked in CI

[xingxue-ibm]

@rustbot label +stable-nominated

[JohnTitor]

Thanks!