re PR fortran/23516 (IMAG is not a generic function when implicit none is declared)

re PR fortran/23516 (IMAG is not a generic function when implicit none is declared)

PR fortran/23516
* intrinsic.c (add_function): Add IMAG, IMAGPART, and REALPART
  intrinsics.
* intrinsic.h: Prototypes for gfc_simplify_realpart and
  gfc_resolve_realpart.
* intrinsic.texi: Document intrinsic procedures.
* simplify.c (gfc_simplify_realpart): New function.
* irseolve.c (gfc_resolve_realpart): New function.

From-SVN: r104537