[Comgr] Use CLANG_LINK_CLANG_DYLIB instead of checking if the clangFrontendTool target exists (#632)

`TARGET clangFrontendTool` was used to check if libclang-cpp was built or not. Instead, use CLANG_LINK_CLANG_DYLIB which is the actual CMake flag that controls if libclang-cpp is built.

Author: jmmartinez

amd/comgr/CMakeLists.txt

@@ -406,7 +406,7 @@ install(FILES
   COMPONENT amd-comgr
   DESTINATION "${CMAKE_INSTALL_LIBDIR}/${AMD_COMGR_PACKAGE_PREFIX}")
 
-if(TARGET clangFrontendTool)
+if(NOT CLANG_LINK_CLANG_DYLIB)
   set(CLANG_LIBS
     clangBasic
     clangDriver