Merge pull request #246 from MrMage/fix-build

Fix building with a clean Xcode and add a CI run to ensure just that.

.gitignore

@@ -3,6 +3,7 @@ project.xcworkspace
 xcuserdata
 DerivedData/
 .build
+build
 /protoc-gen-swift
 /protoc-gen-swiftgrpc
 third_party/**