[bitc-dev] Small build change

[Jonathan S. Shapiro]

The BitC AST is now fairly stable. In order to eliminate the dependency
on ASTmaker for most builds, I've added the ASTMaker output to the
repository. If AST.ast somehow gets a future time stamp it will attempt
to rebuild, but I think that all of the major packaging tools preserve
file timestamps when unpacking. If not, we'll figure something out.

shap