tree-wide: fix a pile of lints

This:
- Converts a bunch of C style casts into C++ casts.
- Removes some very silly pointer subtraction code (which is no more or
  less busted on i686 than it began)
- Fixes some "technically UB" that never had to be UB in the first
  place.
- Makes finally follow the noexcept status of the inner function. Maybe
  in the future we should ban the function from not being noexcept, but
  that is not today.
- Makes various locally-used exceptions inherit from std::exception.

Change-Id: I22e66972602604989b5e494fd940b93e0e6e9297

src/libexpr/eval.cc

@@ -21,7 +21,6 @@
 #include "flake/flakeref.hh"
 
 #include <algorithm>
-#include <chrono>
 #include <iostream>
 #include <sstream>
 #include <cstring>
@@ -146,7 +145,7 @@ bool Value::isTrivial() const
         && internalType != tPrimOpApp
         && (internalType != tThunk
             || (dynamic_cast<ExprAttrs *>(thunk.expr)
-                && ((ExprAttrs *) thunk.expr)->dynamicAttrs.empty())
+                && (static_cast<ExprAttrs *>(thunk.expr))->dynamicAttrs.empty())
             || dynamic_cast<ExprLambda *>(thunk.expr)
             || dynamic_cast<ExprList *>(thunk.expr));
 }