[cxx-interop] Bail if trying to convert call result to void.

Don't try to coerce the result of a call to void. If the "expected"
result type is void, just bail.

Author: zoecarver

lib/IRGen/GenCall.cpp

@@ -1924,6 +1924,9 @@ class SyncCallEmission final : public CallEmission {
     // This can happen when calling C functions, or class method dispatch thunks
     // for methods that have covariant ABI-compatible overrides.
     auto expectedNativeResultType = nativeSchema.getExpandedType(IGF.IGM);
+    // If the expected result type is void, bail.
+    if (expectedNativeResultType->isVoidTy())
+      return;
     if (result->getType() != expectedNativeResultType) {
       result =
           IGF.coerceValue(result, expectedNativeResultType, IGF.IGM.DataLayout);