[WIP] Delayed privatization.

This is a PoC for delayed privatization in OpenMP. Instead of directly
emitting privatization code in the frontend, we add a new op to outline
the privatization logic for a symbol and call-like mapping that maps
from the host symbol to an outlined function-like privatizer op.

Later, we would inline the delayed privatizer function-like op in the
OpenMP region to basically get the same code generated directly by the
fronend at the moment.

Author: ergawy

flang/include/flang/Lower/AbstractConverter.h

@@ -16,6 +16,7 @@
 #include "flang/Common/Fortran.h"
 #include "flang/Lower/LoweringOptions.h"
 #include "flang/Lower/PFTDefs.h"
+#include "flang/Lower/SymbolMap.h"
 #include "flang/Optimizer/Builder/BoxValue.h"
 #include "flang/Semantics/symbol.h"
 #include "mlir/IR/Builders.h"
@@ -296,6 +297,9 @@ class AbstractConverter {
     return loweringOptions;
   }
 
+  virtual Fortran::lower::SymbolBox
+  lookupOneLevelUpSymbol(const Fortran::semantics::Symbol &sym) = 0;
+
 private:
   /// Options controlling lowering behavior.
   const Fortran::lower::LoweringOptions &loweringOptions;

flang/lib/Lower/Bridge.cpp

@@ -1070,7 +1070,7 @@ class FirConverter : public Fortran::lower::AbstractConverter {
   /// Find the symbol in one level up of symbol map such as for host-association
   /// in OpenMP code or return null.
   Fortran::lower::SymbolBox
-  lookupOneLevelUpSymbol(const Fortran::semantics::Symbol &sym) {
+  lookupOneLevelUpSymbol(const Fortran::semantics::Symbol &sym) override {
     if (Fortran::lower::SymbolBox v = localSymbols.lookupOneLevelUpSymbol(sym))
       return v;
     return {};