[CMake] NFC. Add intrinsics_gen target to CMake Exports

By creating a dummy of this target in LLVMConfig.cmake, projects that can build against out-of-tree LLVM can freely depend on the target without needing to have conditionals for if LLVM is in-tree or out-of-tree.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@309389 91177308-0d34-0410-b5e6-96231b3b80d8

cmake/modules/LLVMConfig.cmake.in

@@ -79,5 +79,12 @@ if(NOT TARGET LLVMSupport)
   @llvm_config_include_buildtree_only_exports@
 endif()
 
+# By creating intrinsics_gen here, subprojects that depend on LLVM's
+# tablegen-generated headers can always depend on this target whether building
+# in-tree with LLVM or not.
+if(NOT TARGET intrinsics_gen)
+  add_custom_target(intrinsics_gen)
+endif()
+
 set_property(GLOBAL PROPERTY LLVM_TARGETS_CONFIGURED On)
 include(${LLVM_CMAKE_DIR}/LLVM-Config.cmake)