[flang] [llvm] [flang/flang-rt] Adding support of RAND, IRAND and SRAND intrinsics (PR #166780)

[Kelvin Li via llvm-commits]

kkwli wrote:

I get the same random number with `rand(0)`.
```
$ cat rand.f90
do i=1, 5
  print *, rand(0)
enddo
end

$ bin/flang -frtlib-add-rpath rand.f90

$ a.out
 1.9679691E+09
 1.9679691E+09
 1.9679691E+09
 1.9679691E+09
 1.9679691E+09

```

https://github.com/llvm/llvm-project/pull/166780