IRGen: support the @sensitive attribute

Call `swift_clearSensitive` after destroying or taking "sensitive" struct types.

Also, support calling C-functions with "sensitive" parameters or return values. In SIL, sensitive types are address-only and so are sensitive parameters/return values.
Though, (small) sensitive C-structs are passed directly to/from C-functions. We need re-abstract such parameter and return values for C-functions.

include/swift/Runtime/RuntimeFunctions.def

@@ -2832,6 +2832,13 @@ FUNCTION(ClearSensitive, swift_clearSensitive, C_CC, ClearSensitiveAvailability,
          EFFECT(NoEffect),
          UNKNOWN_MEMEFFECTS)
 
+FUNCTION(MemsetS, memset_s, C_CC, AlwaysAvailable,
+         RETURNS(Int32Ty),
+         ARGS(PtrTy, SizeTy, Int32Ty, SizeTy),
+         ATTRS(NoUnwind),
+         EFFECT(NoEffect),
+         UNKNOWN_MEMEFFECTS)
+
 #undef RETURNS
 #undef ARGS
 #undef ATTRS