py: Fix viper store on x86; add tests for viper ptr16.

tests/micropython/viper_ptr16_store.py

@@ -0,0 +1,19 @@
+# test ptr16 type
+
+@micropython.viper
+def set(dest:ptr16, val:int):
+    dest[0] = val
+
+@micropython.viper
+def memset(dest:ptr16, val:int, n:int):
+    for i in range(n):
+        dest[i] = val
+
+b = bytearray(4)
+print(b)
+
+set(b, 0x4242)
+print(b)
+
+memset(b, 0x4343, len(b) // 2)
+print(b)

tests/micropython/viper_ptr16_store.py.exp

@@ -0,0 +1,3 @@
+bytearray(b'\x00\x00\x00\x00')
+bytearray(b'BB\x00\x00')
+bytearray(b'CCCC')