[flang] Disallow BOZ literal constants as arguments of implicit interfaces

Since BOZ literal arguments are typeless, we cannot know how to pass them as
actual arguments to procedures with implicit interfaces.  This change avoids
the problem by emitting an error message in such situations.

This change stemmed from the following issue --
  flang-compiler#794

Differential Revision: https://reviews.llvm.org/D106831

Author: psteinfeld

flang/lib/Semantics/check-call.cpp

@@ -46,6 +46,9 @@ static void CheckImplicitInterfaceArg(
     }
   }
   if (const auto *expr{arg.UnwrapExpr()}) {
+    if (std::holds_alternative<evaluate::BOZLiteralConstant>(expr->u)) {
+      messages.Say("BOZ argument requires an explicit interface"_err_en_US);
+    }
     if (auto named{evaluate::ExtractNamedEntity(*expr)}) {
       const Symbol &symbol{named->GetLastSymbol()};
       if (symbol.Corank() > 0) {

flang/test/Semantics/boz-literal-constants.f90

@@ -77,4 +77,7 @@ subroutine bozchecks
   res = MERGE_BITS(B"1101",3,B"1011")
 
   res = REAL(B"1101")
+
+  !ERROR: BOZ argument requires an explicit interface
+  call implictSub(Z'12345')
 end subroutine