[gardening] Add a helper to SILFunctionConventions to retrieve if a function has a noreturn result.

Sometimes one just has a SILFunctionConvention instead of the underlying
SILFunctionType (that the SILFunctionConvention contains). This just shims in
that API onto the composition type.

Author: gottesmm

include/swift/SIL/SILFunctionConventions.h

@@ -396,6 +396,9 @@ class SILFunctionConventions {
   /// Return the SIL type of the apply/entry argument at the given index.
   SILType getSILArgumentType(unsigned index,
                              TypeExpansionContext context) const;
+
+  /// Returns true if this function does not return to the caller.
+  bool isNoReturn(TypeExpansionContext context) const;
 };
 
 struct SILFunctionConventions::SILResultTypeFunc {
@@ -464,6 +467,11 @@ SILFunctionConventions::getSILArgumentType(unsigned index,
       funcTy->getParameters()[index - getNumIndirectSILResults()], context);
 }
 
+inline bool
+SILFunctionConventions::isNoReturn(TypeExpansionContext context) const {
+  return funcTy->isNoReturnFunction(silConv.getModule(), context);
+}
+
 inline SILFunctionConventions
 SILModuleConventions::getFunctionConventions(CanSILFunctionType funcTy) {
   return SILFunctionConventions(funcTy, *this);