[fpc-pascal] New feature: IfThen() intrinsic

[Marco van de Voort]

In our previous episode, Sven Barth said:
> After the discussion last year about the inline-if I've decided to add
> it as an intrinsic function instead of an extension of the language.
> Like all intrinsics it's part of the System unit and "declared" like this:
> 
> === code begin ===
> 
> function IfThen(Condition: Boolean; ThenExpr, ElseExpr: type): type;
> 
> === code end ===
> 
> Since it's declared in the System unit it won't interfere with the
> IfThen()s that are declared in the Math unit or other units, so they'll
> continue to work as before to avoid any surprises.
> 
> An important point to note is that in general the result type is
> determined by the ThenExpr (there are a few usability exceptions
> regarding strings and chars).

I'm not really fond of the functionality, and I would not write new code
with it, but it is very handy when converting C code.
 
The only really bad thing is the name, as Florian already said, with the
versions in strutils and math.  The clash with delphi compatible functions
should be avoided.