Built-in abs/min/max for integers; For-loop fixes

tests/compiler/assert.wast

@@ -0,0 +1,45 @@
+(module
+ (type $v (func))
+ (memory $0 1)
+ (data (i32.const 4) "\08\00\00\00")
+ (export "memory" (memory $0))
+ (start $start)
+ (func $start (; 0 ;) (type $v)
+  (if
+   (i32.eqz
+    (i32.const 1)
+   )
+   (unreachable)
+  )
+ )
+)
+(;
+[program.elements]
+  clz
+  ctz
+  popcnt
+  rotl
+  rotr
+  abs
+  ceil
+  copysign
+  floor
+  max
+  min
+  nearest
+  sqrt
+  trunc
+  current_memory
+  grow_memory
+  unreachable
+  load
+  store
+  reinterpret
+  select
+  sizeof
+  isNaN
+  isFinite
+  assert
+[program.exports]
+  
+;)