Fixed a bug in DtoInlineIR

Before this fix, debug info was removed from the module while
parsing inline ir.
Added a check for vector size to gen_gccbuiltins.cpp.

Previously, gen_gccbuiltins was emitting intrinsics
that used vector types larger than 256 bits and those
are not defined in core.simd.
Merge pull request #569 from jerro/bugfix

Bugfix