[lldb][tests] Fix build with LLVM_ENABLE_SWIFT_SUPPORT=OFF

Fix the unittest build when swift support is off.

Author: cachemeifyoucan

lldb/unittests/Core/CMakeLists.txt

@@ -1,3 +1,11 @@
+set(SWIFT_SOURCES
+  SwiftDemanglingPartsTest.cpp
+)
+
+set(LLVM_OPTIONAL_SOURCES ${SWIFT_SOURCES})
+if (NOT LLDB_ENABLE_SWIFT_SUPPORT)
+  unset(SWIFT_SOURCES)
+endif()
 
 add_lldb_unittest(LLDBCoreTests
   DebuggerTest.cpp
@@ -14,9 +22,10 @@ add_lldb_unittest(LLDBCoreTests
   SourceLocationSpecTest.cpp
   SourceManagerTest.cpp
   TelemetryTest.cpp
-  SwiftDemanglingPartsTest.cpp
   UniqueCStringMapTest.cpp
 
+  ${SWIFT_SOURCES}
+
   LINK_COMPONENTS
     Support
     Telemetry