Remove fastmath tests that are defined to be undef/poison

Author: vchuravy

test/fastmath.jl

@@ -60,9 +60,11 @@ fm_fast_64_upd(x) = @fastmath (r=x; r+=eps64_2; r+=eps64_2)
         @test @fastmath(cmp(two,two)) == cmp(two,two)
         @test @fastmath(cmp(two,three)) == cmp(two,three)
         @test @fastmath(cmp(three,two)) == cmp(three,two)
-        @test @fastmath(one/zero) == convert(T,Inf)
-        @test @fastmath(-one/zero) == -convert(T,Inf)
-        @test isnan(@fastmath(zero/zero)) # must not throw
+        # The following operations may yield `undef` (LLVM 11)
+        # or `poison` (LLVM 12+)
+        # @fastmath(one/zero)
+        # @fastmath(-one/zero)
+        # @fastmath(zero/zero)
 
         for x in (zero, two, convert(T, Inf), convert(T, NaN))
             @test @fastmath(isfinite(x))