Type checking of compile time expression has been added to Free Pascal

Compile time expression are used in $IF/$IFC, and under mode MacPas, in $SETC

This should hopefully help everyone to find some errors, but if it makes trouble for anyone please let me know.

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Implementation details:

Each subexpression returns its type to the caller, which then can do type check. Since data types of compile time expressions is not well defined, the type system does a best effort. The drawback is that some errors might not be detected.

Instead of returning a particular data type, a set of possible data types are returned. This way ambigouos types can be handled. For instance a value of 1 can be both a boolean and and integer.

Svn revision 919

Olle Raab