Codegen: More CMake fixes for MacOS native builds

cmake/external_llvm.cmake

@@ -15,10 +15,14 @@ include(ExternalProject)
 
 find_package(LLVM CONFIG)
 
+set(LLVM_PACKAGED FALSE)
+
 if(LLVM_FOUND)
     if(${LLVM_PACKAGE_VERSION} VERSION_GREATER "4.0")
-        message(STATUS "Found LLVM ${LLVM_PACKAGE_VERSION}") 
+        message(STATUS "Found LLVM ${LLVM_PACKAGE_VERSION}")
+        set(LLVM_PACKAGED TRUE)
     else()
+        message(STATUS "Found LLVM ${LLVM_PACKAGE_VERSION} but need atleast 4.0")
         set(LLVM_FOUND FALSE)
     endif()
 endif()
@@ -87,3 +91,4 @@ endif()
 set(LLVM_INCLUDE_DIR ${LLVM_INCLUDE_DIR} PARENT_SCOPE)
 set(LLVM_LIB_DIR ${LLVM_LIB_DIR} PARENT_SCOPE)
 set(LLVM_LINK_LIBS ${LLVM_LINK_LIBS} PARENT_SCOPE)
+set(LLVM_PACKAGED ${LLVM_PACKAGED} PARENT_SCOPE)

src/ngraph/CMakeLists.txt

@@ -159,6 +159,6 @@ install(DIRECTORY
 
 add_dependencies(ngraph eigen)
 
-if(LLVM_INCLUDE_DIR)
+if(NOT LLVM_PACKAGED AND LLVM_INCLUDE_DIR)
     add_dependencies(ngraph ext_llvm)
 endif()