[CMake] Only generate Components.cmake if components are specified

Generating the Components import file is useless if there are no components coming in from the runtimes configuration, so we should skip generation in that case.

This also should fix the configuration error that Renato reported on llvm-dev.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@279893 91177308-0d34-0410-b5e6-96231b3b80d8

runtimes/CMakeLists.txt

@@ -90,25 +90,27 @@ if(${CMAKE_SOURCE_DIR} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR})
   endif()
 
   get_property(SUB_COMPONENTS GLOBAL PROPERTY SUB_COMPONENTS)
-  list(REMOVE_DUPLICATES SUB_COMPONENTS)
-  foreach(component ${SUB_COMPONENTS})
-    if(NOT TARGET ${component})
-      message(SEND_ERROR "Missing target for runtime component ${component}!")
-      continue()
-    endif()
-    if(LLVM_INCLUDE_TESTS AND NOT TARGET check-${component})
-      message(SEND_ERROR "Missing check target for runtime component ${component}!")
-      continue()
-    endif()
-
-    if(TARGET install-${component})
-      list(APPEND SUB_INSTALL_TARGETS install-${component})
-    endif()
-  endforeach()
+  if(SUB_COMPONENTS)
+    list(REMOVE_DUPLICATES SUB_COMPONENTS)
+    foreach(component ${SUB_COMPONENTS})
+      if(NOT TARGET ${component})
+        message(SEND_ERROR "Missing target for runtime component ${component}!")
+        continue()
+      endif()
+      if(LLVM_INCLUDE_TESTS AND NOT TARGET check-${component})
+        message(SEND_ERROR "Missing check target for runtime component ${component}!")
+        continue()
+      endif()
+
+      if(TARGET install-${component})
+        list(APPEND SUB_INSTALL_TARGETS install-${component})
+      endif()
+    endforeach()
 
-  configure_file(
-    ${CMAKE_CURRENT_SOURCE_DIR}/Components.cmake.in
-    ${LLVM_BINARY_DIR}/runtimes/Components.cmake)
+    configure_file(
+      ${CMAKE_CURRENT_SOURCE_DIR}/Components.cmake.in
+      ${LLVM_BINARY_DIR}/runtimes/Components.cmake)
+  endif()
 
 else() # if this is included from LLVM's CMake
   include(${LLVM_BINARY_DIR}/runtimes/Components.cmake OPTIONAL)