flambda-backend: Make float32 NaN quiet (#2670)

* make f32.nan quiet

* add quiet/signal

* macos doesn't return snan

Author: TheNumbat

otherlibs/stdlib_beta/float32.ml

@@ -71,7 +71,9 @@ let one = 1.s
 let minus_one = -1.s
 let infinity = float32_of_bits 0x7f800000l
 let neg_infinity = float32_of_bits 0xff800000l
-let nan = float32_of_bits 0x7f800001l
+let quiet_nan = float32_of_bits 0x7fc00001l
+let signaling_nan = float32_of_bits 0x7f800001l
+let nan = quiet_nan
 let is_finite (x : t) = sub x x = 0.s
 let is_infinite (x : t) = div 1.s x = 0.s
 let is_nan (x : t) = x <> x

otherlibs/stdlib_beta/float32.mli

@@ -128,7 +128,16 @@ val nan : t
     argument returns [nan] as result, unless otherwise specified in
     IEEE 754 standard.  As for floating-point comparisons,
     [=], [<], [<=], [>] and [>=] return [false] and [<>] returns [true]
-    if one or both of their arguments is [nan]. *)
+    if one or both of their arguments is [nan].
+
+    Equivalent to [quiet_nan]. *)
+
+val signaling_nan : t
+(** Signaling NaN. The corresponding signals do not raise OCaml exception,
+    but the value can be useful for interoperability with C libraries. *)
+
+val quiet_nan : t
+(** Quiet NaN. *)
 
 val pi : t
 (** The constant pi. *)