Bugfix

Two bugfixes.

The first bug caused debug info to be removed from the module when inline ir was used.

The second bug was caused by the fact that development version of LLVM supports
some gcc x86 builtins that work on 512 bit vectors, but core.simd only defines 
256 bit vectors. Maybe 512 bit vectors should also be enabled in LDC, but in any case,
gen_gccbuiltins must check for vector size so that it doesn't emit declarations for functions
that work on unsupported types.