[msan] Simplify 'maskedCheckAVXIndexShadow' (#147839)
The current instrumentation has more or and element extraction than a
coal mine:
```
[[TMP10:%.*]] = extractelement <16 x i32> [[TMP9]], i64 0
[[TMP11:%.*]] = and i32 [[TMP10]], 15
[[TMP43:%.*]] = or i32 [[TMP10]], [[TMP11]]
[[TMP12:%.*]] = extractelement <16 x i32> [[TMP9]], i64 1
[[TMP13:%.*]] = and i32 [[TMP12]], 15
[[TMP44:%.*]] = or i32 [[TMP12]], [[TMP13]]
...
[[TMP40:%.*]] = extractelement <16 x i32> [[TMP9]], i64 15
[[TMP41:%.*]] = and i32 [[TMP40]], 15
[[TMP57:%.*]] = or i32 [[TMP40]], [[TMP41]]
[[_MSCMP:%.*]] = icmp ne i32 [[TMP57]], 0
br i1 [[_MSCMP]], label [[TMP102:%.*]], label [[TMP103:%.*]], !prof [[PROF1]]
```
Simplify it to:
```
[[TMP10:%.*]] = trunc <16 x i32> [[T]] to <16 x i4>
[[TMP12:%.*]] = bitcast <16 x i4> [[TMP10]] to i64
[[_MSCMP:%.*]] = icmp ne i64 [[TMP12]], 0
br i1 [[_MSCMP]], label %[[BB13:.*]], label %[[BB14:.*]], !prof [[PROF1]]
```
