[Exclusivity] Put suppression for free function swap() behind a flag

And leave suppression off by default for now. We'll use this to evaluate
how often swap() causes exclusivity conflicts to be reported.

include/swift/AST/SILOptions.h

@@ -143,6 +143,10 @@ public:
   /// Emit compile-time diagnostics when the law of exclusivity is violated.
   bool EnforceExclusivityStatic = false;
 
+  /// Suppress static diagnostics for violations of exclusive access for calls
+  /// to the Standard Library's swap() free function.
+  bool SuppressStaticExclusivitySwap = false;
+
   /// Emit checks to trap at run time when the law of exclusivity is violated.
   bool EnforceExclusivityDynamic = false;