[flang] Accept INDEX(..., BACK=array)

[klausler]

Summary

The intrinsic table entry for INDEX mistakenly required
the optional BACK= argument to be scalar, but it's an
elemental intrinsic that can accept a conforming array.

[PeteSteinfeld]

The change to intrinsics.cpp looks good, but Phabricator thinks that folding05.f90 is a binary file, and I can't create a patched repository with it. Is it possible that there's a weird line ending or and encoding problem in it?

[klausler]

In D117700#3255681, @PeteSteinfeld wrote:

The change to intrinsics.cpp looks good, but Phabricator thinks that folding05.f90 is a binary file, and I can't create a patched repository with it. Is it possible that there's a weird line ending or and encoding problem in it?

This comes up every time I add a test to that file. There are UTF-8 character strings in that test. Can you review based on inspection of the one-word change ("scalar" -> "elemental") in the code?

[PeteSteinfeld]

Thanks for the information about encodings.

All builds, tests, and looks good.

flang/lib/Evaluate/intrinsics.cpp

static const IntrinsicInterface genericIntrinsicFunction[]{
     {"ibits", {{"i", SameInt}, {"pos", AnyInt}, {"len", AnyInt}}, SameInt},
     {"ibset", {{"i", SameInt}, {"pos", AnyInt}}, SameInt},
     {"ichar", {{"c", AnyChar}, DefaultingKIND}, KINDInt},
     {"ieor", {{"i", SameInt}, {"j", SameInt, Rank::elementalOrBOZ}}, SameInt},
     {"ieor", {{"i", BOZ}, {"j", SameInt}}, SameInt},
     {"image_status", {{"image", SameInt}, OptionalTEAM}, DefaultInt},
     {"index",
         {{"string", SameChar}, {"substring", SameChar},
-            {"back", AnyLogical, Rank::scalar, Optionality::optional},
+            {"back", AnyLogical, Rank::elemental, Optionality::optional},
             DefaultingKIND},
         KINDInt},
     {"int", {{"a", AnyNumeric, Rank::elementalOrBOZ}, DefaultingKIND}, KINDInt},
     {"int_ptr_kind", {}, DefaultInt, Rank::scalar},
     {"ior", {{"i", SameInt}, {"j", SameInt, Rank::elementalOrBOZ}}, SameInt},
     {"ior", {{"i", BOZ}, {"j", SameInt}}, SameInt},
     {"ishft", {{"i", SameInt}, {"shift", AnyInt}}, SameInt},
     {"ishftc",