[lldb] Fix cmake logic when no targets are configured

Should fix reported lldb-remote-linux-ubuntu bot post-submit failure

Author: rnk

lldb/unittests/Disassembler/CMakeLists.txt

@@ -19,14 +19,16 @@ if("RISCV" IN_LIST LLVM_TARGETS_TO_BUILD)
   )
 endif()
 
-add_lldb_unittest(DisassemblerTests
-  ${disas_srcs}
-  LINK_LIBS
-    lldbCore
-    lldbSymbol
-    lldbTarget
-    lldbPluginDisassemblerLLVMC
-    lldbPluginProcessUtility
-  LINK_COMPONENTS
-    Support
-    ${LLVM_TARGETS_TO_BUILD})
+if (disas_srcs)
+  add_lldb_unittest(DisassemblerTests
+    ${disas_srcs}
+    LINK_LIBS
+      lldbCore
+      lldbSymbol
+      lldbTarget
+      lldbPluginDisassemblerLLVMC
+      lldbPluginProcessUtility
+    LINK_COMPONENTS
+      Support
+      ${LLVM_TARGETS_TO_BUILD})
+endif()