GitLab

Lepton::ParsedExpression::getConstantValue() used to return NaN to indicate non-constant
expressions. This can break with -ffast-math optimization where NaN comparisons are
not defined.

This patch defines bool isConstant() to test whether an expression is constant before
calling getConstantValue(). getConstantValue() now throws an exception if called on a
non-constant expression.

Clang had been generating the following warning:

```
ParsedExpression.cpp:123:13:
warning:
      30 enumeration values not handled in switch: 'CONSTANT', 'VARIABLE',
      'CUSTOM'...
            [-Wswitch]
                switch (node.getOperation().getId()) {
                                ^
                                1 warning generated.
```

To get rid of this warning, I added a default case, which does nothing.

Lots of new optimizations in ParsedExpression.optimize().  Also optimized CUDA evaluation of expressions.

1) Added DLL export macros to many classes; enough to get tests to compile
2) Cosmetic changes to reduce warnings in Visual Studio:
   a) change many "for (int i ="... to "for (size_t i ="... to avoid unsigned mismatch warnings
   b) included many explicit static_cast<OpenMMReal>() casts to document places where double->float conversion warnings occur