Bug: selection_merge ends block.

[DoeringChristian]

Hi,

I'm writing a SPIR-V Jit and I noticed the following problem.
The SPIR-V specification states for OpSelectionMerge:
"This instruction must immediately precede either an OpBranchConditional or OpSwitch instruction. That is, it must be the second-to-last instruction in its block." The builder however ends the block when calling "selection_merge". When recording a conditional inserting the next operation e.g. OpBranchConditional, the result in the error "Error::MismatchedTerminator" since there is no block selected for the branch operation.

Thanks for your help.