Sprinkle some constexpr around to make Jason happy

Most of these will not matter in practice due to C++14 imposing
significant limitations on what else we can make constexpr, and we cannot
have references outliving the constexpr context either way.

src/catch2/catch_assertion_result.cpp

@@ -11,7 +11,7 @@
 
 namespace Catch {
 
-    AssertionResultData::AssertionResultData(ResultWas::OfType _resultType, LazyExpression const & _lazyExpression):
+    AssertionResultData::AssertionResultData(ResultWas::OfType _resultType, LazyExpression const& _lazyExpression):
         lazyExpression(_lazyExpression),
         resultType(_resultType) {}