[Build] Update SWIFT_TARGET_LIBRARY_NAME for swiftRuntime in new build. (swiftlang#78977)

We need to change `SWIFT_TARGET_LIBRARY_NAME` for the `swiftRuntime`
target in the new build because of changes made to the old build system.

Author: al45tair

Runtimes/Core/runtime/CMakeLists.txt

@@ -86,7 +86,7 @@ endif()
 target_compile_definitions(swiftRuntime
   PRIVATE
     -DSWIFT_RUNTIME
-    -DSWIFT_TARGET_LIBRARY_NAME=swiftRuntime
+    -DSWIFT_TARGET_LIBRARY_NAME=swiftRuntimeCore
     $<$<BOOL:${BUILD_SHARED_LIBS}>:-DswiftCore_EXPORTS>
     $<$<BOOL:${SwiftCore_ENABLE_BACKTRACING}>:-DSWIFT_ENABLE_BACKTRACING>
     $<$<BOOL:${SwiftCore_ENABLE_OVERRIDABLE_RETAIN_RELEASE}>:-DSWIFT_STDLIB_OVERRIDABLE_RETAIN_RELEASE>