Fix DBI loading problem on Linux

Part of PR dotnet#81573 needed to be undone to build libmscordbi.so without
any undefined symbols from the DAC. The DAC_PAL_RegisterModule, etc. stubs I recommended didn't work and DBI
could not be loaded by SOS because of missing exports.

The double pass at the libraries from the `target_link_libraries(mscordbi ${COREDBI_LIBRARIES} ${COREDBI_LIBRARIES})`
cmake file needed to be restored. The stubs were not needed after that.

Author: Mike McLaughlin

src/coreclr/dlls/mscordbi/CMakeLists.txt

@@ -100,7 +100,10 @@ elseif(CLR_CMAKE_HOST_UNIX)
         mscordaccore
     )
 
-    target_link_libraries(mscordbi ${COREDBI_LIBRARIES})
+    # COREDBI_LIBRARIES is mentioned twice because ld is one pass linker and will not find symbols
+    # if they are defined after they are used. Having all libs twice makes sure that ld will actually
+    # find all symbols.
+    target_link_libraries(mscordbi ${COREDBI_LIBRARIES} ${COREDBI_LIBRARIES})
 
     add_dependencies(mscordbi mscordaccore)
 

src/coreclr/dlls/mscordbi/mscordbi.cpp

@@ -32,18 +32,3 @@ BOOL WINAPI DllMain(HINSTANCE hInstance, DWORD dwReason, LPVOID lpReserved)
 	// Defer to the main debugging code.
     return DbgDllMain(hInstance, dwReason, lpReserved);
 }
-
-#if defined(TARGET_LINUX) && !defined(HOST_WINDOWS)
-PALIMPORT HINSTANCE PALAPI DAC_PAL_RegisterModule(IN LPCSTR lpLibFileName);
-PALIMPORT VOID PALAPI DAC_PAL_UnregisterModule(IN HINSTANCE hInstance);
-
-HINSTANCE PALAPI PAL_RegisterModule(IN LPCSTR lpLibFileName)
-{
-     return DAC_PAL_RegisterModule(lpLibFileName);
-}
-
-VOID PALAPI PAL_UnregisterModule(IN HINSTANCE hInstance)
-{
-    DAC_PAL_UnregisterModule(hInstance);
-}
-#endif