Restore behavior (by declaring safe) of these two-arg functions (#440)

Without these dispatches, `can_turbo` will return false for the
two-arg versions of `trunc`, `unsafe_trunc`, `round`, `ceil`, and
`floor`, which follow the form `f(::Type{T}, ::Union{Base.IEEEFloat,
Base.BitInteger64}) where T<:{Union{Base.IEEEFloat, Base.BitInteger64}`
These are well-supported in `VectorizationBase`; moreover,
the 1-arg versions register as safe despite the recent changes.
I have included `convert` and `reinterpret` in this list, as they
happen to follow the same form, and are also well-supported.

Author: andrewjradcliffe

src/LoopVectorization.jl

@@ -114,6 +114,9 @@ using Base.Meta: isexpr
 using DocStringExtensions
 import LinearAlgebra # for check_args
 
+using Base:
+  unsafe_trunc
+
 using Base.FastMath:
   add_fast,
   sub_fast,

src/condense_loopset.jl

@@ -922,6 +922,10 @@ can_turbo(::typeof(^), ::Val{2}) = true
 can_turbo(::typeof(Base.literal_pow), ::Val{3}) = true
 can_turbo(::typeof(Base.FastMath.pow_fast), ::Val{2}) = true
 
+for f ∈ (convert, reinterpret, trunc, unsafe_trunc, round, ceil, floor)
+    @eval can_turbo(::typeof($f), ::Val{2}) = true
+end
+
 """
     check_turbo_safe(ls::LoopSet)