[ABI] Added signedAsData bit to method descriptor flags.

It is necessary to determine whether a given method in a vtable or a
witness table ought to be signed as data or as code.  For example, async
functions pointers must be signed as data.

Author: nate-chandler

include/swift/ABI/MetadataValues.h

@@ -317,6 +317,7 @@ class MethodDescriptorFlags {
     KindMask = 0x0F,                // 16 kinds should be enough for anybody
     IsInstanceMask = 0x10,
     IsDynamicMask = 0x20,
+    IsSignedAsDataMask = 0x40,
     ExtraDiscriminatorShift = 16,
     ExtraDiscriminatorMask = 0xFFFF0000,
   };
@@ -345,6 +346,15 @@ class MethodDescriptorFlags {
     return copy;
   }
 
+  MethodDescriptorFlags withIsSignedAsData(bool isSignedAsData) const {
+    auto copy = *this;
+    if (isSignedAsData)
+      copy.Value |= IsSignedAsDataMask;
+    else
+      copy.Value &= ~IsSignedAsDataMask;
+    return copy;
+  }
+
   MethodDescriptorFlags withExtraDiscriminator(uint16_t value) const {
     auto copy = *this;
     copy.Value = (copy.Value & ~ExtraDiscriminatorMask)
@@ -362,6 +372,8 @@ class MethodDescriptorFlags {
   /// Note that 'init' is not considered an instance member.
   bool isInstance() const { return Value & IsInstanceMask; }
 
+  bool isSignedAsData() const { return Value & IsSignedAsDataMask; }
+
   uint16_t getExtraDiscriminator() const {
     return (Value >> ExtraDiscriminatorShift);
   }
@@ -527,6 +539,7 @@ class ProtocolRequirementFlags {
   enum : int_type {
     KindMask = 0x0F,                // 16 kinds should be enough for anybody
     IsInstanceMask = 0x10,
+    IsSignedAsDataMask = 0x20,
     ExtraDiscriminatorShift = 16,
     ExtraDiscriminatorMask = 0xFFFF0000,
   };
@@ -546,6 +559,15 @@ class ProtocolRequirementFlags {
     return copy;
   }
 
+  ProtocolRequirementFlags withIsSignedAsData(bool isSignedAsData) const {
+    auto copy = *this;
+    if (isSignedAsData)
+      copy.Value |= IsSignedAsDataMask;
+    else
+      copy.Value &= ~IsSignedAsDataMask;
+    return copy;
+  }
+
   ProtocolRequirementFlags withExtraDiscriminator(uint16_t value) const {
     auto copy = *this;
     copy.Value = (copy.Value & ~ExtraDiscriminatorMask)
@@ -560,6 +582,8 @@ class ProtocolRequirementFlags {
   /// Note that 'init' is not considered an instance member.
   bool isInstance() const { return Value & IsInstanceMask; }
 
+  bool isSignedAsData() const { return Value & IsSignedAsDataMask; }
+
   bool isSignedWithAddress() const {
     return getKind() != Kind::BaseProtocol;
   }