Enable API stability checking for standard library on arm64

This test was only enabled for x86_64.

Author: DougGregor

test/api-digester/Outputs/stability-stdlib-source-arm64.swift.expected

@@ -1,8 +1,15 @@
+#include "stability-stdlib-source-base.swift.expected"
+
+// NOTE: Most differences from the baseline are common across all architectures
+// should go into stability-stdlib-source-base.swift.expected. Only capture
+// arm64-specific differences from the x86_64 baseline here.
+
 Constructor BinaryFloatingPoint.init(_:) has been removed
 Constructor Double.init(_:) has parameter 0 type change from Swift.Float80 to Swift.Float16
-Constructor Double.init(exactly:) has parameter 0 type change from Swift.Float80 to Swift.Float16
+Constructor Double.init(exactly:) has parameter 0 type change from Swift.Float80 to Source
 Constructor Float.init(_:) has parameter 0 type change from Swift.Float80 to Swift.Float16
-Constructor Float.init(exactly:) has parameter 0 type change from Swift.Float80 to Swift.Float16
+Constructor Float.init(exactly:) has parameter 0 type change from Swift.Float80 to Source
+Constructor Float.init(exactly:) has generic signature change from to <Source where Source : Swift.BinaryInteger>
 Constructor Int.init(_:) has parameter 0 type change from Swift.Float80 to Swift.Float16
 Constructor Int.init(exactly:) has parameter 0 type change from Swift.Float80 to Swift.Float16
 Constructor Int16.init(_:) has parameter 0 type change from Swift.Float80 to Swift.Float16
@@ -25,3 +32,4 @@ Constructor UInt8.init(_:) has parameter 0 type change from Swift.Float80 to Swi
 Constructor UInt8.init(exactly:) has parameter 0 type change from Swift.Float80 to Swift.Float16
 Struct Float80 has been removed
 TypeAlias CLongDouble has underlying type change from Swift.Float80 to Swift.Double
+Constructor Double.init(exactly:) has generic signature change from to <Source where Source : Swift.BinaryInteger>