compiler: fix unreachable type assert

The unreachable instruction is actually a block terminator so may only
be inserted at the end of a basic block. This is not always the case for
type asserts, so don't insert this instruction.

LLVM will hopefully optimize it anyway when it realizes anything after
the panic() call is unreachable.

compiler.go

@@ -2345,7 +2345,6 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
 				} else {
 					fn := c.mod.NamedFunction("runtime.interfaceTypeAssert")
 					c.builder.CreateCall(fn, []llvm.Value{commaOk}, "")
-					c.builder.CreateUnreachable()
 					return undef, nil
 				}
 			}