[flang] Update extensions doc for DO loop over REAL

Original-commit: flang-compiler/f18@bc8ea466fcd129b895288b4c6c1ac81336e54dab
Reviewed-on: https://github.com/flang-compiler/f18/pull/455
1 file changed
tree: c2167f50f1bdf647c5a2e090b4da4d104148a93f
  1. flang/