[flang] add QSORT extension intrinsic to the runtime

[jeanPerier]

Add support for legacy Fortran intrinsic QSORT from lib3f (used to be described in section 3f of the man pages. The best documentation I could find online is https://docs.oracle.com/cd/E19205-01/820-4180/man3f/index.html).

Since I do not think there is any standard sorting intrinsic in Fortran, this is still a relevant extension.

Example usage:

integer function  icompar(a,b)
 integer :: a, b
 icompar = merge(-1, merge(0, 1, a.eq.b), a.lt.b)
end function

  external :: icompar
  integer :: x(10) = [2,1,10,8,9,5,3,4,6,7]
  call qsort(x, 10,4, icompar)
  print *, x
end

[jeanPerier]

For the record, here is another link to documentation for the 3F library https://docs.nvidia.com/hpc-sdk/pgi-compilers/20.4/x86/fortran-ref-guide/index.htm#fort-3f-routines