Remove extra semicolons after macro invocation.

Silences some Clang warnings.
Revert meaning of AddExp/MinExp for pointers to DMD default.

It might be worth considering to move the stride multiplication
down to the glue layer in the upstream sources. But assigning a
different meaning to AST nodes was a giant maintenance
liability, especially with regard to CTFE.
Add virtual destructor to EnclosingHandler to silence warnings.
Re-enable SymOffExp and remove associated LLVM-only modifications.
Merge pull request #391 from klickverbot/symoffexp

Re-enable SymOffExp.