[Runtime] Expose the protocol conformance state as a _swift_debug variable.

Have Remote Mirror look that up instead of the C++ mangled name.

rdar://problem/55481578

Author: mikeash

include/swift/Reflection/ReflectionContext.h

@@ -818,12 +818,20 @@ class ReflectionContext
 
   llvm::Optional<std::string> iterateConformances(
     std::function<void(StoredPointer Type, StoredPointer Proto)> Call) {
-    std::string ConformancesName = "__ZL12Conformances";
-    auto ConformancesAddr = getReader().getSymbolAddress(ConformancesName);
+    std::string ConformancesPointerName =
+      "__swift_debug_protocolConformanceStatePointer";
+    auto ConformancesAddrAddr =
+      getReader().getSymbolAddress(ConformancesPointerName);
+    if (!ConformancesAddrAddr)
+      return "unable to look up debug variable " + ConformancesPointerName;
+
+    auto ConformancesAddr =
+      getReader().readPointer(ConformancesAddrAddr, sizeof(StoredPointer));
     if (!ConformancesAddr)
-      return "unable to look up conformances cache symbol " + ConformancesName;
+      return "unable to read value of " + ConformancesPointerName;
 
-    auto Root = getReader().readPointer(ConformancesAddr, sizeof(StoredPointer));
+    auto Root = getReader().readPointer(ConformancesAddr->getResolvedAddress(),
+                                        sizeof(StoredPointer));
     iterateConformanceTree(Root->getResolvedAddress().getAddressData(), Call);
     return llvm::None;
   }

include/swift/Runtime/Debug.h

@@ -237,6 +237,9 @@ bool _swift_debug_metadataAllocationIterationEnabled;
 SWIFT_RUNTIME_STDLIB_SPI
 const void * const _swift_debug_allocationPoolPointer;
 
+SWIFT_RUNTIME_STDLIB_SPI
+const void * const _swift_debug_protocolConformanceStatePointer;
+
 SWIFT_RUNTIME_ATTRIBUTE_ALWAYS_INLINE
 inline static int swift_asprintf(char **strp, const char *fmt, ...) {
   va_list args;

stdlib/public/runtime/ProtocolConformance.cpp

@@ -315,6 +315,9 @@ void ConformanceState::verify() const {
 
 static Lazy<ConformanceState> Conformances;
 
+const void * const swift::_swift_debug_protocolConformanceStatePointer =
+  &Conformances;
+
 static void
 _registerProtocolConformances(ConformanceState &C,
                               const ProtocolConformanceRecord *begin,