With this, you can check enums with Type::tint32, instead of constructing the enum type. For example: `checkStructElems(sle, {Type::tint32})` for this UDA:
```
enum E {a,b,c};
struct exampleUDA
{
E e;
}
```
The part needing most attention was ddmd.root.ctfloat, ddmd.target (incl.
gen/target.cpp) and ddmd.builtin. The front-end is now prepared for
elaborate compile-time floating-point types to allow for proper cross-
compilation.
This version still uses the host's `real` type for compile-time reals,
except for MSVC hosts, which still use 64-bit doubles (when compiled with
DMD host compiler too).
Some other changes:
* semantic*() of Statements extracted from statement.d to statementsem.d
* mangle() -> mangleToBuffer()
* Identifier::string -> toChars()
* Token::float80value => floatvalue
* Dsymbol::isAggregateMember() => isMember()
* BoolExp is no more
* ddmd.root.ctfloat: LDC-specific CTFE builtins
This now uses actual struct literals for attributes that can be generated
by arbitrary CTFE expressions. This should allow for quite a bit of
flexibility when targeting multiple compilers.
