[fpc-pascal] undocumented 'library' hint directive

[Marco van de Voort]

In our previous episode, Graeme Geldenhuys said:
> > http://docwiki.embarcadero.com/RADStudio/Seattle/en/Declarations_and_Statements
> 
> To follow on from your quotes....
> 
> I guess with the above description IFDEF's will most likely be the
> better option in real-world code.

Those were always more to aid with the VCL->CLX transition or cohabitation.

Those share many common method names, but directives like this allowed to
ban/flag some of them (like gethandle, windowhandle etc), making it easier
to upgrade/prepare vcl codebases to CLX.

Deprecated and platform are a bit more generic.

Experimental is mainly to make absolutely clear that not anything published
is definitive. IMHO should be used more often.