[flang][nfc] Fix comments, remove needless API, tweak script

* Remove an unimplemented and unused member function declaration
* Remove a misleading comment about an unrelated constraint number
* Fix a comment
* Add f18 crash message to "flang" driver script

Differential Revision: https://reviews.llvm.org/D95180

flang/include/flang/Parser/provenance.h

@@ -173,7 +173,6 @@ public:
   std::string GetPath(Provenance) const; // __FILE__
   int GetLineNumber(Provenance) const; // __LINE__
   Provenance CompilerInsertionProvenance(char ch);
-  Provenance CompilerInsertionProvenance(const char *, std::size_t);
   ProvenanceRange IntersectionWithSourceFiles(ProvenanceRange) const;
   llvm::raw_ostream &Dump(llvm::raw_ostream &) const;
 

flang/include/flang/Semantics/symbol.h

@@ -356,7 +356,7 @@ private:
 };
 
 // Record the USE of a symbol: location is where (USE statement or renaming);
-// symbol is the USEd module.
+// symbol is in the USEd module.
 class UseDetails {
 public:
   UseDetails(const SourceName &location, const Symbol &symbol)

flang/lib/Semantics/assignment.cpp

@@ -70,7 +70,7 @@ void AssignmentContext::Analyze(const parser::AssignmentStmt &stmt) {
       const Scope &scope{context_.FindScope(lhsLoc)};
       if (auto whyNot{WhyNotModifiable(lhsLoc, lhs, scope, true)}) {
         if (auto *msg{Say(lhsLoc,
-                "Left-hand side of assignment is not modifiable"_err_en_US)}) { // C1158
+                "Left-hand side of assignment is not modifiable"_err_en_US)}) {
           msg->Attach(*whyNot);
         }
       }

flang/tools/f18/flang

@@ -12,4 +12,9 @@ module_dir=$wd/include/flang
 if [[ ! -d $module_dir ]]; then
   module_dir=$wd/tools/flang/include/flang
 fi
-$wd/bin/f18 -module-suffix .f18.mod -intrinsic-module-directory $module_dir "$@"
+opts="-module-suffix .f18.mod -intrinsic-module-directory $module_dir"
+if ! $wd/bin/f18 $opts "$@"
+then status=$?
+     echo flang: in $PWD, f18 failed with exit status $status: $wd/bin/f18 $opts "$@" >&2
+     exit $status
+fi