Export witness table and RTTI objects in compiled libraries. (#1514)

* Export witness table objects in compiled code.

- Ensure that witness tables are preceeded with `extern "C"` modifier in the generated C++ code.
- RTTI objects use the mangled name of the type directly, so that can be queried using the type's mangled name directly from the resulting DLL.
- Expose `Linkage::getTypeConformanceWitnessMangledName` to return the mangled name of witness tables to the host.
- Ensure that all witness tables (including those for associated types) have proper mangled name.

* Fix GCC error in Slang generated code.

1 files changed, 2 insertions, 0 deletions

diff --git a/source/slang/slang-check-decl.cpp b/source/slang/slang-check-decl.cpp
index f9a514d23..4fa5fff17 100644
--- a/source/slang/slang-check-decl.cpp
+++ b/source/slang/slang-check-decl.cpp
@@ -2450,6 +2450,7 @@ namespace Slang
         {
             witnessTable = new WitnessTable();
             witnessTable->baseType = DeclRefType::create(m_astBuilder, interfaceDeclRef);
+            witnessTable->witnessedType = type;
         }
         context->mapInterfaceToWitnessTable.Add(interfaceDeclRef, witnessTable);
 
@@ -3021,6 +3022,7 @@ namespace Slang
             //
             RefPtr<WitnessTable> witnessTable = new WitnessTable();
             witnessTable->baseType = enumConformanceDecl->base.type;
+            witnessTable->witnessedType = enumTypeType;
             enumConformanceDecl->witnessTable = witnessTable;
 
             Name* tagAssociatedTypeName = getSession()->getNameObj("__Tag");