[SystemZ][z/OS] Fix warnings from unsigned int to long in 32-bit mode

This patch fixes the warnings which shows up when libcxx library started to be compiled in 32-bit mode on z/OS.
More specifically, the assignment from unsigned int to time_t aka long was flags as follows:
 ```
libcxx/include/c++/v1/__support/ibm/nanosleep.h:31:11: warning: implicit conversion changes signedness: 'unsigned int' to 'time_t' (aka 'long') [-Wsign-conversion]
  __sec = sleep(static_cast<unsigned int>(__sec));
        ~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
libcxx/include/c++/v1/__support/ibm/nanosleep.h:36:36: warning: implicit conversion changes signedness: 'unsigned int' to 'long' [-Wsign-conversion]
      __rem->tv_nsec = __micro_sec * 1000;
                     ~ ~~~~~~~~~~~~^~~~~~
libcxx/include/c++/v1/__support/ibm/nanosleep.h:47:36: warning: implicit conversion changes signedness: 'unsigned int' to 'long' [-Wsign-conversion]
      __rem->tv_nsec = __micro_sec * 1000;
                     ~ ~~~~~~~~~~~~^~~~~~
3 warnings generated.
```

Here is a small test case illustrating the issue:

```
typedef long    time_t ;
unsigned int sleep(unsigned int );
int main() {
  time_t sec = 0;
#ifdef FIX
  sec = static_cast<time_t>(sleep(static_cast<unsigned int>(sec)));
#else
  sec = sleep(static_cast<unsigned int>(sec));
#endif
}
```
clang++ -c -Wsign-conversion -m32 t.C
```
t.C:8:9: warning: implicit conversion changes signedness: 'unsigned int' to 'time_t' (aka 'long') [-Wsign-conversion]
  sec = sleep(static_cast<unsigned int>(sec));
      ~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Reviewed By: ldionne, #libc, Quuxplusone, Mordante

Differential Revision: https://reviews.llvm.org/D112837

0 files changed, 0 insertions, 0 deletions