Rob Loach 395f925941
libretro-common: Fix redefinition warnings of _POSIX_C_SOURCE (#15748)
Small fix to only define `_POSIX_C_SOURCE` if it's not already defined.

```
rthreads/rthreads.c:25: warning: "_POSIX_C_SOURCE" redefined
```
2024-05-16 16:05:58 -04:00
..
2023-02-23 13:15:14 +01:00
2023-02-23 13:15:14 +01:00