Fixes issue #131; because they weren't being marked as internal before, when
compiling to multiple targets these would lead to multiply-defined symbols.
Now, the Linker::LinkModules() call doesn't link in any functions
marked as 'internal', which is problematic, since we'd like to have
just about all of the builtins marked as internal so that they are
eliminated after they've been inlined when they are in fact used.
This change removes all of the internal qualifiers in the builtins
and adds a lSetInternalFunctions() routine to builtins.cpp that
sets this property on the functions that need it after they've
been linked in by LinkModules().
