Add check for redefining types.

examples/sysir/typeerr1.janet

@@ -0,0 +1,15 @@
+(def ir-asm
+  @{:instructions
+   '(
+     # Types
+     (type-prim Real f32)
+     (type-prim 1 s32)
+
+     (bind bob Real)
+
+     (return bob))
+   :parameter-count 0
+   :link-name "redefine_type_fail"})
+
+(def as (sysir/asm ir-asm))
+(print (sysir/to-c as))