与OpenMP相关的错误，以及使用OpenMP构建LLVM / Clang时C++

我正在尝试从Fedora 25的源代码编译LLVM，Clang，OpenMP(来自LLVM项目(和libc++(libcxx(。默认的GCC 6.3用于构建它们。我发出

cmake ../llvm -DCMAKE_BUILD_TYPE=Release -DLLVM_TARGETS_TO_BUILD="X86"

一切似乎都很顺利，直到我得到

-- Performing Test LIBOMPTARGET_HAVE_STD_CPP11_FLAG
-- Performing Test LIBOMPTARGET_HAVE_STD_CPP11_FLAG - Success
-- Performing Test LIBOMPTARGET_HAVE_WERROR_FLAG
-- Performing Test LIBOMPTARGET_HAVE_WERROR_FLAG - Success
-- Could NOT find LIBOMPTARGET_DEP_LIBELF (missing:  LIBOMPTARGET_DEP_LIBELF_LIBRARIES LIBOMPTARGET_DEP_LIBELF_INCLUDE_DIRS) 
-- Found PkgConfig: /usr/bin/pkg-config (found version "0.29.1") 
-- Could NOT find LIBOMPTARGET_DEP_LIBFFI (missing:  LIBOMPTARGET_DEP_LIBFFI_LIBRARIES LIBOMPTARGET_DEP_LIBFFI_INCLUDE_DIRS) 
-- LIBOMPTARGET: Building offloading runtime library libomptarget.
-- LIBOMPTARGET: Not building aarch64 offloading plugin: machine not found in the system.
-- LIBOMPTARGET: Not building CUDA offloading plugin: libelf dependency not found.
-- LIBOMPTARGET: Not building PPC64 offloading plugin: machine not found in the system.
-- LIBOMPTARGET: Not building PPC64le offloading plugin: machine not found in the system.
-- LIBOMPTARGET: Not building x86_64 offloading plugin: libelf dependency not found.
-- Found Z3: /usr/lib64/libz3.so (found suitable version "4.5.0 - 64 bit - build hashcode d57a2a6dce92", minimum required is "4.5") 
-- Looking for sys/resource.h
-- Looking for sys/resource.h - found
-- Clang version: 5.0.0
-- Performing Test CXX_SUPPORTS_NO_NESTED_ANON_TYPES_FLAG
-- Performing Test CXX_SUPPORTS_NO_NESTED_ANON_TYPES_FLAG - Failed
-- Configuring done
-- Generating done

似乎有两个错误 - 一个与OpenMP有关(与LIBOMPTARGET_DEP_LIBELF和LIBOMPTARGET_DEP_LIBFFI有关(，1个与C++有关(CXX_SUPPORTS_NO_NESTED_ANON_TYPES_FLAG - Failed(。我真的不知道它们是什么意思，但我希望能够至少在多核 CPU 上使用 OpenMP，并且我绝对希望能够编译C++源文件。那么我应该如何关注这些错误呢？如果它们很重要，有什么提示可以在这里做什么吗？

更新：当我尝试构建它时，我在libcxx中得到了几个未定义的引用。