Sweep out some extra warnings

Swept:
`-Wpadded` in some places (where it caused extra size, instead of just
saying "hey, we padded struct at the end to align, just as standard says")
`-Wweak-vtables` everywhere (Clang)
`-Wexit-time-destructors` everywhere (Clang)
`-Wmissing-noreturn` everywhere (Clang)

The last three are enabled for Clang compilation going forward.

Also enabled `-Wunreachable-code` for Clang and GCC

include/internal/catch_assertionresult.cpp

@@ -10,8 +10,8 @@
 
 namespace Catch {
     AssertionResultData::AssertionResultData(ResultWas::OfType _resultType, LazyExpression const & _lazyExpression):
-        resultType(_resultType),
-        lazyExpression(_lazyExpression) {}
+        lazyExpression(_lazyExpression),
+        resultType(_resultType) {}
 
     std::string AssertionResultData::reconstructExpression() const {